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COPHHGHT DEPOSIT. 



MACHINE DRAWING 



A PRACTICAL GUIDE TO THE STANDARD METHODS OF 

GRAPHICAL REPRESENTATION OF MACHINES, 

INCLUDING COMPLETE DETAIL DRAWINGS 

OF A DUPLEX PUMP AND OF A 

DIRECT-CURRENT GENERATOR 



By CHARLES L. GRIFFIN, S.B. 

ASSISTANT ENGINEER, THE SOLVAT PROCESS COMPANY 
AMERICAN SOCIETY OF MECHANICAL ENGINEERS 



AND 

C. C. ADAMS, B.S. 

SWITCHBOARD ENGINEER WITH GENERAL ELECTRIC COMPANT 



ILLUSTRATED 



> t > 



AMERICAN TECHNICAL SOCIETY 

CHICAGO 

1914 



TJ"£30 
£■87 



COPYRIGHT, 1914, BY 

AMERICAN TECHNICAL SOCIETY 



COPYRIGHTED IN GREAT BRITAIN 
ALL RIGHTS RESERVED 




OCT" -7 1914 

CI.A380846 



CONTENTS 



PAGE 



Working drawings 1 

Definition of 1 

Lines 2 

Arrangement of views \ 4 

Sectional views 5 

Shade lines 7 

Dimensions 9 

Classes of Workmen using drawings 11 

Specifications for screw threads 15 

Specifications for bolts and nuts 20 

Specifications for pipes and pipe threads 26 

Scale drawings : 27 

Details of preparation 31 

Pencil drawing 31 

Tracing 32 

Blue printing 33 

Illustrative drawings 37 

Crank 37 

Bell crank 41 

Rocker arm and pin 42 

Link stud 43 

Flange coupling. 43 

Clamp eye 45 

Connecting rod 46 

Gear with split hub 46 

Spur gear 49 

Pair of beveled gears 49 

Worm and worm gear. 49 

Cylinder head 52 

Water cylinder for triplex pump 53 

Hoisting drum 56 

Crane drum grooved for chain. 56 

Detail of ordinary shaft 59 

"Broken" pieces and "out-of-scale" dimensions 60 

Bearing stand with cap and boxes removed 60 



2 CONTENTS 



PAGE 



Working drawings 

Sample letters 61 

Drawing room practice 62 

Plates 63 

Mechanism drawing 69 

Helix 70 

Screw threads 75 

Cams 82 

Belting 108 

Gears 132 

Plates 149 

Working shop drawings — mechanical 157 

Plan and scope of advanced work 157 

Essential requirements 159 

Duplex pump plates 163 

Steam end layout 165 

Steam cylinder 171 

Piston rod and valve stem 184 

Steam chest and valve 186 

Valve motion layout 189 

Valve motion details 193 

Yoke, stuffing boxes, bracket, etc 195 

Water end layout 199 

Water cylinder 201 

Water cylinder cap and air chamber 204 

Plunger and valve details 206 

Foundation 208 

General drawing 208 

Order sheets 211 

Shop drawings — electrical 219 

Requirements 219 

Essentials of a good drawing 220 

Design of a direct-current generator 222 

Material supplied to designing draftsman 222 

Preliminary layout sketch 224 

General outline drawing 224 



CONTENTS 3 

PAGE 

Design of a direct-current generator 

Details of armature and commutator .224 

Armature punchings 226 

Armature windings 226 

Armature flanges and spider 230 

Equalizer rings and support 231 

Commutator details 233 

Armature shaft. . '. 238 

Details of field frame and coils 238 

Magnet frame and base 240 

Pole pieces 241 

Main field coils and spools 245 

Commutating field coils and spools 246 

Details of brush rigging 249 

Brush holder, stud and connections 249 

Brush holder yoke and brush shifting device 253 

Bearings and pedestals 255 

Split bearings for armature shaft 255 

Pedestals and caps for bearings : . . . . 257 

Details of electrical connections 259 

Assembly of connections 259 

Connections 262 

Final assembly drawing 262 

Outline 262 




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INTRODUCTION 

1 I 'HE ability to visualize a piece of machinery, to arrive at 
A the exact idea of the designer or the inventor, and then 
to draw these details in such a clear and concise form as to make 
them thoroughly understood is a very important attribute in 
the manufacturing world. The pattern maker must have just 
the views and dimensions of the machine that will enable him to 
make accurate patterns for the cast parts. The shopman must 
be furnished with every detail which he should know in order 
to finish the pieces to proper dimensions; he must be told just 
what surfaces to leave rough, which ones to machine in the lathe, 
and which ones to caliper to thousandths of an inch. It is evident, 
that the machine draftsman who is to do his work with the highest 
efficiency must not only be able to draw accurately, but he must 
thoroughly understand the machines which he is called upon 
to represent. 

<I To one who understands "reading drawings", a well-made 
set of specifications is really a work of art, and it is the aim of 
the publishers of this little volume to put in the hands of those 
who are only moderately schooled in the art of mechanical drawing 
the means of developing themselves in the broader art of machine 
drawing. The subject has been developed very logically, starting 
first with the presentation of the details and the conventional 
Ways of representing the parts of simple machines, followed by 
standard methods of working out such mechanisms as screws, 
pulleys, cams, gears, etc. Finally, complete detailed drawings 
are furnished and exhaustively discussed in connection with the 
designs of a duplex pump and of a direct-current generator. 
The presentation is exceedingly practical and will appeal to men 
who are interested in either the mechanical or electrical fields. 
The plates are complete in themselves, but if a person wishes to 
obtain the maximum benefit from his study he may work out 
enlarged drawings to scale without any additional details. 



MACHINE DRAWING 

PART I 



WORKING DRAWINGS 

METHODS AND CONVENTIONS 

In Mechanical Drawing, Parts I, II, and III, the common 
drafting instruments and materials are described, and hints given 
regarding their use; the fundamental geometrical problems are solved; 
the principles of orthographic projection are stated, and their appli- 
cation to intersections and developments illustrated. A careful 
study of these Parts, with the actual drawing work incident thereto, 
should have given the student considerable facility in producing 
good line work ; he should now be able to draw neatly and accurately 
any simple piece which may be given him, correctly applying the 
principles as described. 

In producing working drawings the principles already laid 
down are constantly used, and the more they are at the finger ends 
of the student the easier his work will become. The principles of 
projection must be thoroughly understood and fixed in the student's 
mind in order that he may devote himself with the greatest applica- 
tion to the actual detail of the drawing, and he must not be com- 
pelled at every step to turn back to find out how to make the simple 
projections. 

Definition of Working Drawings. A working drawing is a 
drawing which completely instructs the workman, so that he is able 
actually to make in the shop the object which the drawing repre- 
sents; in other words, a working drawing conveys to the mechanic 
all the information necessary to make the object. The student 
should constantly keep before him the idea that the workman must 
take a drawing, and, without any further instructions verbal or 
written, produce the object as the draftsman intended it to be 
made. The instruction supplied by the drawing should not only 
cover the form and size of the object, but also the kind of material 
of which it is to be made, the number of pieces desired, and the 



2 MACHINE DRAWING 

finish of its surfaces. A drawing, therefore, is a sort of abbreviated 
language, or shorthand method of conveying an amount of exact, 
detail information, which it would take many pages of manuscript 
to convey. 

A second point to be noted in connection with a working draw- 
ing is that the workman has no time to puzzle over a mass of lines 
and figures more complicated than necessary. This means that 
special attention must be paid to making the drawing as simple as 
possible; all lines and figures which are unnecessary, beyond the 
point of conveying complete information, are hindrances rather 
than helps to the workman; moreover, it takes the draftsman's 
time to make these extra lines and figures, and thus the drawing 



FULL LINE FOR 
GENERAL DRAWING. 



FULL LINE FOR 
'DETAIL DRA WING. 

DOTTED LINES FOR 
INVISIBLE PARTS. 

• CENTER LINE. 

.DIMENSION AND 
EXTENSION LINES. 
" (USE EITHER) 

- SHADE LINES. 



Fig. 1. Conventional Lines Used in Machine Drawings 

becomes unnecessarily expensive. A good drawing, therefore, not 
only implies accuracy and completeness but also simplicity and direct- 
ness. 

Lines. The secret of a clear drawing, as far as the line work 
is concerned, lies not only in absolute uniformity in the making of 
the lines, but in choosing certain characteristic lines to convey differ- 
ent ideas. The most common kinds of lines used are shown in Fig. 1 
and described below, and the purposes of their use are stated. 

Full Lines. Full lines represent the portions of the object 
which are visible; they should be bold and clear, heavy on detail 
drawings, say ^" wide, and lighter on an assembled drawing. 

Invisible Lines. Invisible lines represent the hidden parts of 
the object; they consist of short dashes regularly spaced, the spaces 



MACHINE DRAWING 3 

being about J the length of the dash ; the dashes should never have 
a greater width than that of the full line, and usually should be 
slightly less. A drawing is much easier to read if the full lines force 
themselves on the eye, while the dotted lines, by their lighter char- 
acter, are left in the background. 

Center or Axis Lines. Center or axis lines consist of alternate 
long and short dashes, finer than the main lines of the drawing. 




Fig. 2. Flanged Coupling Giving Practical Application of Fig. 1 



Some draftsmen prefer not to use "dash and dot" center lines, but 
make them continuous fine lines. Either style is good. 

Dimension and Extension Lines. Dimension and extension 
lines are made fine, like center lines, and may be either full or dotted, 
according to the preference of the draftsman; the full line is prefer- 
able on account of its bolder character and the shorter time it takes 
to make it. 

Extension lines start a short distance away from the edges of 
the object, so as to break up the continuity of the lines of the object 
and the extension line. 

Dimension lines are run between the extension lines, terminating 
at the extension lines in arrows. The extension lines should always 
run a short distance beyond the point at which the dimension line 
touches them. 



MACHINE DRAWING 



Shade Lines. Shade lines are used for the purpose of more 
clearly bringing out to the eye the projecting edges of the object on 
the shadow side, and should be the heaviest lines on the drawing; 
the proper effect is secured if these lines are made nearly twice as 
heavy as the principal lines of the drawing. 

Fig. 2 shows a flanged coupling in which the lines given in Fig. 1 
are applied to an actual problem. In the lower half of the elevation 
observe how the invisible parts are shown by dotted lines* 

Arrangement of Views. Imagine a rectangular block placed 
within a glass box, and the surfaces projected to the top, front and 

right-hand side, as in Fig. 3; now 
open the box in the manner indi- 
cated in Fig. 4 and we have three 
views of the object on a plane 
surface, i.e., the drawing paper of 
the draftsman. These views are 
called top plan, front, and side 
elevations respectively, and are 
denoted in the figure by the let- 
ters T, F, and S. If more views 
are required, the arrangement is 
shown in Fig. 5. The bottom 
plan B is found below the front elevation, and the left side eleva- 
tion S' is found on the left of the 
front elevation, the same princi- 
ples of projection being used as 
in the former case. 

The above procedure is 
equivalent to tracing on each side 
of the box the outline of the ob- 
ject as observed by the eye, when 
directly in front of each side of 
the object; after this is done the 
unfolding of the box results in the 
outlines shown in Fig. 4. 

If we consider the front ele- 
vation of the object as our starting point, then the top plan is 
above, the bottom plan below, the view of the right-hand side is on the 




Fig. 3. Rectangular Block Within a Glass 
Box, the Surfaces Projected to the Top, Front, 
and Right-Hand Side 




Fig. 4. First and Preferred Method of Show- 
ing Top, Front, and Right-Hand Side Views of 
a Rectangular Block on a Plane Surface 



MACHINE DRAWING 



T 
S* ' F S 

B 



Fig. 5. Method of Showing Five Views of a 
Rectangular Block on a Plane Surface 



right of, and the view of the left-hand side is on the left of the front 
elevation. This arrangement of views is easily remembered and is 
very logical; it is the most common method of projection in drafting 
work, and will be used throughout this book. For such a simple 
object as that considered above, two views only are necessary, a 
front elevation and top plan, but machine drawings frequently require 
three views, top, front, and side, and sometimes more. 

Some draftsmen prefer the 
method of projection shown in 
Fig. 6, by which the lines of the 
object, instead of being observed 
through an imaginary glass parti- 
tion and traced thereon, are pro- 
jected away from the eye upon 
surfaces beyond the object; the 
surfaces are then unfolded as be- 
fore, with the result, as shown in 
Fig'. 7, that the front elevation, 
being the starting point, the top 
plan is below, the bottom plan is above, the left-hand view is at the 
right of, and the right-hand view is at the left of the front elevation. 
This system of projection has few advantages for machine drawing, 
and has been largely superseded by the former method. 

Sectional Views. The inte- 
rior construction of machine 
parts, especially if at all compli- 
cated, can seldom be clearly or 
completely shown by dotted 
lines. A large number of dotted 
lines on a drawing is very con- 
fusing, and in many cases ren- 
ders the drawing useless. Sec- 
tional views are used to over- 
come this difficulty, and as an 
unlimited number of sections 
can be taken, it is always possi- 
ble to make clear the interior construction of any piece, however 
complicated. 




Fig. 6. Second Method of Showing an Object 
and Its Projections in Vertical and Horizontal 
Planes 

(Not Advised for Machine Drawing) 



6 MACHINE DRAWING 

Crosshatching. To make a sectional view, the object is supposed 
to be cut open, and all the material removed between the cutting 
plane and the eye. This makes visible the hidden portion, and the 
drawing, therefore, consists of full lines made the same as any other, 
except that the material which was cut by the plane is "cross- 
hatched". Crosshatching consists of drawing medium width lines, 
regularly spaced, across the cut surface, the lines usually being at 
an angle of 45° with the horizontal. In case of two adjoining sur- 
faces being cut, the lines are sloped to the right and left, respectively. 

The butt joint given in Fig. 8 shows the use of crosshatching 
when the section taken is through different pieces of the same mate- 



FRONT ELEVATION 




















V 


















H 


















■ 


r 0P PLAN 







Fig. 7. Second Method of Projection, 

Planes Unfolding 
{Not Advised for Machine Drawing) 



Fig. 8. Butt Joint Showing Use of Cross- 
hatching When Section Is Through Differ- 
ent Pieces of One Material 



rial. Notice the different angles at which the section lines are 
drawn for each separate piece. 

It is often convenient to show the kind of material of the object 
by the style of crosshatching. The conventional styles generally 
used are illustrated in Fig. 9. It is quite general, however, to use 
the plain form (as for cast iron), and call for the material by a specific 
note, thus leaving no possible doubt of the material required, and 
simplifying the labor of crosshatching, which is a tedious process at 
best. The distance between the lines should be as wide as possible, 



MACHINE DRAWING 



to save labor, and yet bring out the surface clearly. A good average 
spacing is about -^" '. Fig. 10 shows the end of a connecting rod. 
The section shows the different materials of which the object is 
made, cast iron, brass, steel, and babbitt. 







CAST 7/70// 



WROUGHT IRON. 



STEEL 



CQMP OR 3F/ASS 






WW 


PIPI 




'////////, 



LEAD OH BABB/T 



V//LCAN/TE WOOD 

Fig. 9. Conventional Representation of Materials 



3ft/CK 



Shade Lines. The theoretical principles for shade lines, already 
given in Mechanical Drawing, Part III, cannot be exactly applied 
to working machine drawings without involving an excessive amount 
of time and labor. The conventional rule, therefore, has been 




Fig. 10. End of Connecting Rod Showing Crosshatching When Section Is Through Different 

Materials 

established that shade lines may be used for all lower and right-hand 
projecting edges. By "projecting edges" are meant edges of surfaces 
which are not flush with adjoining surfaces, but which project above 
them, or are in a plane nearer the eye. All views of an object are 



8 



MACHINE DRAWING 



treated alike, the ray of light casting the shadow being supposed 
to come from the upper left-hand corner of the drawing. The 

contour lines of cylinders, cones, 
* and other rounded surfaces, if 

'projecting, are- shaded the same 
as sharp edges. 

Uses. Shade lines, when 
used, are for the specific purpose 
of relieving the flatness of draw- 
ing, and represent a purely con- 
ventional means of indicating to 
the eye projecting surfaces, i.e., 
surfaces which are in different 
planes parallel to the eye. 
Whether the surfaces be curved 
or flat, as long as they are pro- 
jecting, or in front of other surfaces, is of no moment, for the effect 
desired is the same for both, namely, the separation of the surfaces. 
Applications in Practical Work. Few drawing offices allow 
shade lines to be used on regular detail machine work on account of 
the extra labor required and the loss of accuracy in the drawing by 
the use of a wide line. For general or "show" drawings, where the 
i effect of separating the surfaces 



Fig. 11. 



Direction of Light Rays and Loca- 
tion of Shade Lines 





is desired, thus bringing out more 
clearly the relation of the parts, 
the use of shade lines is occasion- 
ally permitted. The draftsman 
should know how to apply them 
when required, and Figs. 11 to 16 
illustrate their use. 

Shade- Line Methods . Fig . 1 1 
shows the assumed direction of 
the ray of light in each of the 
three views. The piece should be 
inked in with the usual standard 
width of line, then gone over the second time, making the extra 
width for the shaded lines on the inside of the proper lines. This 
leaves the outside measurement of the piece unchanged for possible 



Fig. 12. 



Location of Shade Lines for Piece 
with Hole 



MACHINE DRAWING 



scaling. Some draftsmen claim that they can make the heavy 
shade lines as they go along, thus avoiding the second inking, but 
in the long run it will be found that time will be saved, more uniform 
lines and fewer blots made, if the 
process of shading be accom- 
plished by a second inking. 

Fig. 12 is similar to Fig. 11 
but with a hole instead of a lug, 
and the difference in shade lines 
should be noted. 

Fig. 13 is the same as Fig. 
11 with a round boss and the 
lower right-hand corner rounded. 

Fig. 14 is a plain washer, 
Fig. 15 a common hexagonal nut. 

Fig. 16 is a washer or disk 
with a shaft in it. The right- 
and left-hand views are shown to bring out the point that the shaft 
projecting on the right has its end shaded, while on the left, being 
flush with the face of the disk, it is not shaded. 




Fig. 13. Location of Shade Lines for 
Rounded Corner 





r 



Fig. 14. Location of Shade Lines for 
Circular Piece 



Fig. 15. Location of Shade Lines for 
Hexagonal Piece 



Dimensions. It is easy to spoil an otherwise good drawing by 
loose and careless methods of putting on dimensions. Systematic 
and careful effort must constantly be used to make every dimension 



10 



MACHINE DRAWING 



upon a drawing absolutely clear. To put it still more strongly, it 
must be absolutely impossible for any dimension of a drawing to 
raise doubt in the workman's mind as to its meaning. The drafts- 
man has no justifiable excuse for mistakes in the shop due to poorly 
made dimension lines or small and blotted figures. 

The arrows terminating the dimension lines should be pointed, 
bold, and regular, thus, (— — ^f — *\ 9 not like this, h — &j~ — H. The 
arrow points should exactly touch the extension lines, thus, 
h — s£ » | , not like this, h — *£- — H. The figures should be broad, 
bold, and clear, and of good size to be easily read. A gap may be 
left for the figure, thus, \+ — j/" — ►], or the line may run straight 




Fig. 16. Location of Shade Lines for Disk with Shaft 



through, thus, 
the line thus,^. 



rS!L 



—I, or the figures may be placed wholly above 



la. 



A* 



It should be noted that by making figures broad, they will 
appear bold and clear, even when they are limited to small height. 
The common error of making them narrow destroys their bold char- 
acter, and renders them difficult to read. Note the difference between 
the following examples, both sets of figures being exactly the same 
height, but one broad and the other narrow, fig as riots . 

Fractions should always have the dividing line horizontal, 
thus, V~wA not like this, H^J. 

Small dimensions, or dimensions in cramped places should be 
made thus, *| (~|" or Jjfcg" or -|gf~ • 



MACHINE DRAWING 11 

For distances greater than 36 inches, and often for distances 
greater than 12 inches, the dimensions are usually given in feet and 
inches. These dimensions should be indicated thus, |- — *'-$'^H, the 
dash being made bold and conspicuous. 

COMPLETE INSTRUCTIONS AND SPECIFICATIONS 

It is naturally difficult for the student to determine what con- 
stitutes "complete instructions to the workman", and this knowl- 
edge can only be fully acquired by experience, both in drawing 
room and shop. Association, however, with the shop men who use 
drawings, a careful observation of their operation of tools, and a 
general familiarity with handling of material in a shop, help wonder- 
fully in getting the right point of view and proper spirit for making 
a good drawing. When one stops to think about it, to give instruc- 
tions without having the least idea of how the workman will go about 
it to follow them, seems the height of foolishness, yet that is what 
the student who tries to make working drawings wholly from book 
rules is doing. He should use his book knowledge as a guide and 
constant help, but he should be a "shop man" first, last, and all the 
time. When he has acquired the habit of constantly putting himself 
in the workman's place, his drawings will be right and will convey 
"complete instructions to the workman." 

Classes of Workmen Using Drawings. In the ordinary run of 
shop work there are several classes of workmen who have to use 
drawings. Broadly classed, they are as follows: 

Pattern makers, Blacksmiths, Machinists (including Tool- 
makers, Special Machine men, and Erectors), Order and Receiving 
Clerks. 

These several workmen will use the same drawing, and the 
instruction which it conveys must be so arranged that each can 
readily pick out the portion which he needs to enable his 
work to be properly done. The general requirements of each are 
discussed below and form the basis for the style and methods of 
dimensioning drawings used in common practice, and illustrated in 
this book. 

Pattern Maker. The pattern maker, on receiving a detail 
drawing of a piece, first proceeds to copy it full size, divided up into 
such sections as are convenient, upon his work board. This board 



12 MACHINE DRAWING 

is merely a large smooth table top, set up on a couple of horses. 
Sometimes brown paper is tacked on this board and the pattern 
drawing made on it, but more often the pencil lines are made directly 
on the surface of the board and the board resurfaced for future work. 
He does not make a finished drawing, but with his straight-edge, 
large dividers, and compasses he lays out enough to enable him to see 
and measure the detail at all points. 

This pattern layout is made for a number of reasons. Molten 
cast iron, when it cools, shrinks about J" per foot, so the pattern 
has to be made larger than the figures on the drawing call for. In 
order to save calculation for each dimension, a "shrink rule" is used, 
each foot of which is made 12 §" long. The pattern maker 
uses this rule in all his work, and thus makes his layout on a "shrink" 
basis. 

Wherever the drawing calls for finished surfaces, the stock of 
the pattern has to be increased by J" or more, and this addition 
has to show on the pattern maker's drawing. In order to get the 
casting out of the sand of the mold, "draft", or taper on the pattern, 
has to be allowed. As the draftsman cannot always predict just 
how the piece will be molded, the "draft" is not shown on the office 
drawing, and the pattern maker, therefore, has to make the allow- 
ance and show it on his drawing. All fillets, sizes of cores and core 
prints, details of core boxes, and loose pieces of the pattern have to 
be carefully worked up on the pattern drawing. The result of this 
special pattern layout often is that certain minor changes have to 
be made in the shape and size of the piece to permit the pattern to 
be properly built and readily molded in the foundry, for a good pat- 
tern maker has also to be a good foundryman. We thus see that, 
as far as the pattern maker is concerned, the drawing must be very 
complete as to detail, both inside and out, and carry dimensions for 
all surfaces, cores, fillets, corners, etc. 

These dimensions must be in even figures as far as possible, as 
a pattern maker's rule seldom reads finer than te". Gear work 
is a specialty, and decimals are allowable, and there are certain other 
cases where odd dimensions cannot be avoided. In arranging the 
dimensions on the drawing, the more knowledge the draftsman has 
of pattern making, the more conveniently will he figure the drawing 
for the pattern maker. He will, in figuring the interior of a casting, 



MACHINE DRAWING 13 

think of the core box which will be made, and will be sure that he 
gives the length, breadth, and depth of the cavity, and all corners, 
bosses, and lugs projecting into it, with simplicity and clearness. 
He will give dimensions for all sloping lines and odd-shaped curves 
definitely and carefully, thinking all the while of the pattern maker 
and his tools, the square, straight-edge, dividers, and compasses. 
He will avoid thin edges, and frail projections, and awkward inter- 
sections. The consideration of such points as these is what makes 
a good drawing for the pattern maker to use, and greatly reduces 
the cost of the pattern, for pattern making is relatively high-priced 
labor. Some of these points are really points of machine design, 
but it is not possible for a good detail drawing to be made without 
using to a small extent, at least, the elementary principles of design. 
These the student can unconsciously acquire by familiarizing himself 
with actual shop work. 

Blacksmith. The blacksmith sometimes uses a pattern for a 
forging. This is to enable him to lay aside the drawing for pieces 
which are to be made in large numbers, and set his calipers quickly 
and accurately from a pattern. Simplicity of shape is of even more 
importance to the blacksmith than to the pattern maker. The 
stock material of the blacksmith consists of straight bars of iron and 
steel of round, square, and oblong cross section. All bosses, lugs, 
hubs, or sudden variations of shape have to be produced by "up- 
setting" or welding, either of which is a process involving time, care, 
and expense. Forgings, therefore, should be, as far as possible, 
simple, straight pieces, with few bosses or lugs, and when bends are 
necessary they should be of the simplest nature. 

In forging a piece the blacksmith has to work quickly, and has 
no time to read or measure fine dimensions, it is therefore useless to 
expect him to read any finer dimensions than ^"; special atten- 
tion should be paid to giving him over-all dimensions, not only for 
cutting off the stock, but for enabling him to make his measure- 
ments quickly while the piece is hot and gripped by his tongs on the 
anvil. The blacksmith has to make about the same allowance of 
extra stock for finished surfaces as the pattern maker. 

Machinist The machinist uses only a few of the figures on the 
average drawing, while the pattern maker and blacksmith use prac- 
tically all of them. The machinist is concerned only with finishing 



14 MACHINE DRAWING 

the piece, and views the drawing with regard to the machine work 
upon it. In order to finish the surfaces accurately in proper relation 
to one another it is necessary to choose some fundamental face of 
the piece, first finish that, and then use it as a gauging surface from 
which to work the others. The draftsman, if he is reasonably 
familiar with shop work, can usually foresee what this gauging 
surface will be. This has an important influence on his dimensions, 
for he should so give the dimensions that the machinist will find 
them convenient and consistent with all his operations on the piece. 

When special tools, jigs, fixtures, and automatic devices are 
applied for the finishing of pieces in large numbers, the method of 
dimensioning is apt to be somewhat different from that on the gen- 
eral run of machine work. A free use of notes on the drawing, speci- 
fying the nature of finished surface desired, or the kind of fit, or any 
special points in connection with the machining of the piece, is 
valuable to the machinist. It is not good economy to spend any 
more labor on securing a finished surface than the purpose for which 
it is made requires. For example, in turning up a shaft with a 
number of bearings along it, most of its surface being free, care 
should be taken to finish the parts for the bearings to an exact diam- 
eter, but for the balance of the length a smooth surface with the 
diameter reasonably accurate is all that is necessary. The drawing 
should specify this difference of finish so that the machinist will not 
waste time on the piece. 

The special operations on a piece, such as cutting of gear teeth, 
grinding and "lapping" of shafts, cutting of threads, etc., are all 
done subsequent to the main finishing of the piece. For example, 
the casting for a cut gear is first bored, the hub faced, and the solid 
rim turned and faced to the dimensions on the drawing. This pro- 
duces the "gear blank". The subsequent operations of cutting the 
teeth on an automatic gear-cutting machine, and key seating the hub 
on a keyseater, require additional instructions as to the style of 
cutter, number of teeth, dimensions and style of keyway, etc. 

Machine shops are differently equipped for doing the same 
kinds of work, and this has an important influence on the manner 
of placing the finishing dimensions on drawings. Thus, some shops 
have rotary planers instead of the regular reciprocating platen type. 
Some have turret lathes, screw machines, and horizontal boring 



MACHINE DRAWING 15 

mills, while others have only lathes. Some have grinding machines, 
both for flat surface and cylindrical work, the final finishing cuts 
being taken on these machines, after the pieces have been roughed 
out on the lathe and planer. Grinding machines are now regularly 
built to take a heavy cut and coarse feed for roughing out the work, 
thus often dispensing entirely with the lathe. Milling machines, 
though found in all shops, are used in widely different scopes. Some 
use the milling machine almost entirely, to the exclusion of the 
planer, specially heavy machines being adapted for this purpose. 
Locomotive shops differ in their equipment and practice from sta- 
tionary engine shops ; machine tool and automatic machinery builders 
have little in common with the equipment of shops for manufacturing 
heavy power transmission machinery; steam pump shops are wholly 
different in their equipment from that of an establishment building 
electrical machinery. 

All these differences have an important bearing on the style of 
drawings needed, and especially so on the methods of giving the 
dimensions for the use of the machinist. Without attempting to 
give an idea of how to control each case, which would be well nigh 
impossible, suffice it to say that the student should become impressed 
w T ith the fact that he must study the workman constantly in order to 
be able to give him upon the drawing the necessary "complete 
instructions". 

Order and Receiving Clerks. The order and receiving clerks are 
very easily satisfied as far as their part in the use of a working 
drawing is concerned. They simply need a designating mark, a 
pattern number for a casting, and a piece number for all other parts, 
together with the material and number wanted of each piece, in 
order that the proper orders may be written, and the material 
identified for recording its receipt in the shop or field. The number 
wanted is often given only on a separate "bill of material" which 
accompanies the drawing, but it is also quite general to note on the 
drawing in the title of each piece, the number wanted for one com- 
plete machine, whether billed elsewhere or not. 

Specifications fcr Screw Threads. Exact drawings for the helix 
forming the thread of a screw are shown in Machine Drawing, Part 
II. These not only are difficult to draw, but they consume con- 
siderable time to produce accurately, therefore draftsmen have 



16 



MACHINE DRAWING 



adopted certain conventions to represent the thread on working 
drawings. Some of these conventions are shown in Fig. 17. Here 
a represents a single, right-hand, square thread; b, a single, right- 
hand, sharp V thread, and its modifications, the United States 
Standard or Seller's thread, and the Whitworth thread; c represents 
a left-hand, sharp thread ; d is the most common convention for any 
thread of a V=shaped cross section; e for any thread on a very small 
bolt or set screw;/ is a modification of d, there being no slope to the 
thread, which convention is preferred by some draftsmen; g repre- 




f^^^ 



f-"^ 



Fig. 17. Conventional Representations of Screw Threads 



sents a standard pipe thread, the taper on the sides of the pipe being 
neglected. 

There are other conventions for threads in use, but the above 
are the most important ones. These certainly can not be mistaken 
for anything else, which is the real test for any conventional repre- 
sentation of an object. 

Pitch. The pitch of a screw thread is the distance between 
corresponding points on two successive threads measured parallel 
to the axis. A small axial section is shown at D on the thread a. 
The square groove, which gives the thread its name, has a depth 
equal to about J the pitch. Starting at the bottom, and following 
the edge of a thread in making one turn around the bolt, or from A 
to B on the front and B to C on the rear, we find that the thread 
advances parallel to the axis a distance AC, or the pitch. As we 



MACHINE DRAWING 17 

can see but one half of a turn it will be noted that a single right-hand 
thread advances a distance equal to | the pitch along the right-hand 
side, and similarly for a single left-hand thread, the distance ad- 
vanced would be \ the pitch on the left-hand side. The slope is, 
therefore, upward and to the right in the first case, and upward and 
to the left in the second case. 

Drawing Thread. To draw the thread, space off the sides of 
the bolt with the dividers set to \ the pitch, determine the slope, 
whether for single, double, or triple thread, and fill in the tops of the 
threads. The depth of the thread, say \ the pitch, should then be 
laid off on each side and the lines drawn which show the visible 
portion of the bottom of the thread, thus completing the view for 
the ordinary convention. When the slope is considerable, as in this 
case, a small portion of the rear thread becomes visible, and may be 
shown. 

For the thread at b it will be readily seen that an axial section 
would give V grooves, and as the standard angle for the grooves of 
the thread in this country is 60°, the projections are equilateral 
triangles. As before, if we follow a thread around the bolt, or from 
E to F on the front, and F to G on the back, we find for the single 
thread screw that the visible portion of the thread EF advances 
along the right-hand side a distance equal to J the pitch. Hence 
starting at the bottom, laying off the distance KF equal to | the 
pitch on the right-hand side, and connecting E to F, we have the 
slope of the thread determined. Spacing the pitch on the left-hand 
side for such distance as is required, we may then draw through 
these points lines parallel to EF, or the top lines of the thread. The 
V's may then be drawn with the aid of a T square and 30° triangle, 
after which the bottom of the threads may be connected. It will 
be noted that the top of the thread on one side is directly opposite 
the bottom of the thread on the other side. The left-hand V thread 
at c is drawn in a similar way to b, the thread advancing on the left- 
hand side instead of on the right. 

Considerable care is required to get the V's uniform, and the 
more practical, usual, and in nearly all cases satisfactory method of 
showing the thread is given in the remaining figures. 

Tiie spacing for the conventions d, e, and / approximates the 
pit jh of the thread, and time can be saved by the draftsman learning 



18 



MACHINE DRAWING 




Fig. 18. Conventional Drawing for 
Threads in Sectional Pieces 



to space with the eye rather than with the dividers. The light lines 
representing the top of the thread should be drawn first, the heavier 
lines for the bottom of the thread are then drawn midway between 
the light lines, stopping a short distance from the edges of the bolt. 
Often no difference in width is made between the lines representing 
the top and bottom of the threads, thus still further simplifying the 
conventional representation. It is well for the beginner to draw 
pencil lines limiting the bottom of the thread, so that the ends of 
the heavy lines will not be ragged or irregular. It rather improves 
the appearance of the thread to have the slant exaggerated in d, e, 
and g. 

Threads in Sectional Pieces. Figs. 18, 19, and 20 illustrate 
the common method of representing threads when they occur in 

pieces which are drawn in cross sec- 
tion. The front half of the piece is 
supposed to be removed and we are 
looking at the back half. Now the 
thread on the back side of a screw 
slants the opposite way from the 
way it slants on the front side, and of course the same is true 
of the thread in a tapped hole. Consequently, since it is the 
back side of the hole which is seen, the slant of the lines which repre- 
sent the thread is opposite to the direction they would have were 
we looking at the front side of the screw which goes into the hole. 
We have just learned that for a right-hand thread on a screw the 
lines slant upward from left to right, and therefore for a right-hand 
thread seen on the back side of a tapped hole, the lines will slant 
upward from right to left. In other words, for a right-hand thread 
in a hole which comes in a cross section, the lines slant the same as 
they would on the front of a left-hand thread on a bolt; and for a 
left-hand thread in a sectioned hole, the slant is the same as for a 
right-hand thread on a bolt. 

Fig. 19 is a piece which has a smooth hole through it and a 
thread on the outside. Here the entire thread is invisible, except 
at the contour of the cylinder, and must be indicated by the notches. 
These are drawn by spacing off the distance which is used for the 
pitch and from the points thus found drawing lines with the triangle 
which make an angle of 60° with the axis of the cylinder. For a 



MACHINE DRAWING 



19 



TABLE I 
United States Standard Screw Threads 





- 

Diameter 


Threads 


Diameter 


Threads 


Diameter 


Threads 


of Bolt 


per Inch 


of Bolt 


per Inch 


of Bolt 


per Inch 


1 

4 


20 


5 

8 


11 


If 


6 


5 

16 


18 


3 
4 


10 


U 


6 


3 

8 


16 


7 
8 


9 


1 5 

x 8 


51 . 


7 
16 


14 


1 


8 


x 4 


5 


1 
2 


13 


n 


7 


1^ 


5 


9 
16 


12 


n 


7 


2 


4-i 

^2 



TABLE II 
Whitworth Standard Screw Threads 





Diameter 


Threads 


Diameter 


Threads 


Diameter 


Threads 


of Bolt 


per Inch 


of Bolt 


per Inch 


of Bolt 


per Inch 


l 

4 


20 


5 
8 


11 


If 


6 


5 
16 


18 


3 
4 


10 


14 


6 


3 

8 


16 


7 
8 


9 


1 8 


5 


7 
16 


14 


1 


8 


■•■4 


5 


1 

2 


12 


1* 


7 


1 ^ 
x 8 


*2 


9 
16 


12 


u 


7 


2 


4 1 

^2 




single thread the notches on one side have their outer points oppo- 
site the inner points of the notches on the other side. For a double 
thread the notches are directly opposite each 
other. 

Fig. 20 shows two ways of quarter-section- 
ing a threaded piece, the only difference being 
that on one the contour of the sectional part is 
drawn a straight line, while on the other the con- 
tour is notched. Either one may be used. The 
straight contour can, of course, be drawn much 
more quickly and in places where there is no danger of sacri- 
ficing clearness it should be used for that reason. If the draw- 
ing is somewhat complicated, so that without the notches it might 
not be quite clear that the piece was threaded, the notches should 
be used. 

As has already been suggested, the student will doubtless find 
many other customs in the matter of drawing threads which are 



Fig. 19. Conven- 
tional Drawing for 
Threads in Sectional 
Pieces 



20 



MACHINE DRAWING 



quite as good as the above. These have been given as ones which 
are common, and easily drawn. As a matter of convenience 
Tables I and II are given, which show the number of threads per 

inch on some of the most com- 
mon sizes of bolts, according to 
the standard adopted by the 
United States Government, and 
the Whitworth or English stand- 
ard. 

Specifications for Bolts and 
Nuts. A bolt is a cylindrical bar 
upset at one end to form a head 
and having a screw thread cut at the other end. 

A nut is a hollow piece of metal in which a screw thread has been 
cut. 

A right-hand bolt has its thread so cut that its nut goes on, or 
advances along the axis of the bolt, when turned in the same direc- 
tion as the hands of a watch. A left-hand bolt has its thread so cut 





Fig. 20. 



Conventional Drawing for Threads 
in Sectional Pieces j 




Fig. 21. Conventional Drawing for Machine Bolt and Nut 



that its nut must be turned opposite to the hands of a watch in order 
to have it go on. 

Hexagonal Bolt Head and Nut. Figs. 21 and 22 show con- 
ventional drawings of a f-inch machine bolt having a hexagonal 
head and nut. The head is simply a hexagonal prism which has 
been chamfered, i.e., the corners rounded off so that the top view 
shows a circle inscribed in a hexagon, see Fig. 23. This top view 
has been omitted in Figs. 21 and 22, the conventional drawing being 
considered sufficient to show that the head is hexagonal, yet some 



MACHINE DRAWING 



21 



draftsmen prefer to specify whether the head and nut are hexagonal 
or square, thus, "SQ.HD.", "HEX. N." In this case the view across 




Fig. 22. Conventional Drawing for Machine Bolt and Nut 

the long diameter is given in preference to the view across the 
flats, so that in close quarters the clearance of the corners may be 
readily seen. The shank of the bolt is represented as explained 





Fig. 23. Conventional Drawing~for Machine Bolt Head 

above for conventional threads. The point is chamfered a little in 
the figure so that it appears as the frustum of a cone. 

Another style of point is shown in Fig. 24, where the end is 




*<s c 

Fig. 24. Conventional Drawing for Machine Bolt 

rounded off with a radius equal to about \\ times the diameter. 
The lines which represent the thread should not cross the line drawn 
square across the bolt where the chamfer or rounding of the point 



22 



MACHINE DRAWING 



begins. Note that in Fig. 21 the threads have been shown dotted 
through the nut, while in Fig. 22 the simpler and more common 
method is followed of omitting the dotted threads and showing the 
long diameter of the nut. 

The dimensions given are all that are necessary for the work- 
man to make a standard bolt and nut. Some draftsmen prefer to 
show the length of bolt and thread from the base of the frustum or 
spherical end, as in Fig. 22, but this does not at once give the total 
length under the head, which is usually the important figure. In 
case dimensions for the head are needed the thickness and the 




Fig. 25. Machine Bolt with U. S. Standard Thread 



distance across flats should be given, as obtained from the table of 
proportions on page 25. If standard threads are not used, then the 
number of threads per inch must be given. 

A method for making a conventional drawing of a hexagonal 
bolt head or nut is shown in Fig. 24. From A as a center describe 
an arc with a radius equal to the diameter of the bolt, making it 
intersect the perpendicular to the center line through A at points 
B and C. Continue the sides of the bolt until they intersect the 
arc at E and F, and draw lines through B and C parallel to sides 
of bolt. Draw a tangent to the arc parallel to BC for the top of the 
head. Find by trial the radius G and draw the arcs for the sides 
of the head. It will be noted that the long diameter of the hexagon 
by this method is twice the diameter of bolt, which is practically 



MACHINE DRAWING 



23 



HE 



true to the standard table for bolts under 1-inch diameter, and suffi- 
ciently exact for the larger sizes in common use. 

Fig. 25 is a drawing to scale of a 24-inch rough bolt, having a 
hexagonal head and United States standard thread. Dimensions for 
the height and width of the head have been taken from table of bolt 
heads on page 25. The width of the head, 3f ", is the diameter 
of the chamfer circle and is the first portion of the plan view to be 
drawn. Then the hexagon is circumscribed about the chamfer 
circle. Project the width of the faces and BD for the flat portion of 
the top. Assuming the chamfer to be conical and at 45° with the 
axis, draw lines BC and DF. The curves of intersection are approxi- 
mated by arcs of circles springing from F and C and drawn tangent 
to BD. 

The enlarged thread section below shows that the thread is 
flattened at top and bottom by cutting off J of the depth F of the V 
thread. Note that the pitch 
of the thread is laid off on a 
line located outside of the true 
diameter of the bolt by an 
amount equal to the portion 
cut off the ordinary sharp V 
thread. The end is rounded 
with a radius equal to the 
diameter, or preferably 1| times the diameter of the bolt. 

Two views, plan and elevation, of two faces of a hexagonal bolt 
head are given in Fig. 23. The chamfer circle is tangent to the 
sides of the hexagon, which means that the tool, in making the cham- 
fer, cuts off the corners of the top as at ABC. The true curves 
DAB and BCE are lines of intersection of a cone or sphere with 
a hexagonal prism and may be easily obtained by the principles of 
projection. A simpler and much more convenient method is to 
approximate these curves with arcs of circles, using the height of 
the head as a radius, as shown. 

In case it is desired to show more chamfer as in Fig. 26, the 
top of the head may be cut off at FK and Gil at an angle of 30° 
or 45°, and the diameter of the chamfer circle is projected to the plan 
view as shown. The width of the hexagon is the same as before 
and is readily projected from the plan view. The curves of inter- 




K D 



Fig. 26. Hexagonal Bolt Head with Chamfer 



24 



MACHINE DRAWING 



section DAB and BCE are drawn as arcs of circles, but instead 
of being tangent to the top they are tangent to the line KH, which 

indicates the place where 
the chamfer cuts the flat 
sides of the hexagon. 

Square Head and Nut- 
Fig. 27 shows three views 
of a square head or nut 
with chamfer corresponding 
to that on the hexagonal 
head in Fig. 23; and Fig. 28 
shows the square head or 
nut chamfered to correspond 
to Fig. 26. Referring first 
to Fig. 27, the arc on the 
side view which shows the 
short diameter of the nut is drawn with a radius A, equal to two 
and one-quarter times the diameter of the bolt on which the head 
or nut belongs. The arcs on the other side view are drawn with a 
radius B } equal to one-half of A. The lines EF are drawn from 




Fig. 27. Three Views of Square Head or Nut 
with Chamfer 




Fig. 28. Three Views of Square Head or Nut with Chamfer 



points E tangent to the arcs, and it will be found that the points of 
tangency will come almost at the points where the arcs cut the 



MACHINE DRAWING 25 

TABLE III 

Rough Square and Hexagon Bolt Heads. U. S. Standard 

(franklin institute) 



Diameter 


Width of 


Thickness 


Diameter 


Width of 


Thickness 


of Bolt 


Head 


of Head 


; of Bolt 


Head 


of Head 


1 


i 


i 


1 


1 £ 

1 8 


1 3 


4 


2 


4 


16 


5 


19 


19 


11 


1U 


29 


16 


32 


64 


32 


3 

8 


11 
16 


11 

32 


H 


2 


1 


7 


25 


25 


H 


0_3_ 
^ 16 


1-3- 

1 32 


16 


32 


64 


1 


7 


7 


H 


2 1 


1 -3- 
1 16 


2 


8 


16 


9 
16 


31 
32 


31 
64 


i^ 

x 8 


0_9_ 

■^16 


1-2- 

1 32 


5 

8 


1ft 


1 7 
32 


x 4 


2! 


1 a 


3 

4 


n 


5 
8 


1^ 


O 15 
■^16 


1 15 

x 32 


7 


1ft 


23 

32 


2 


3| 


1 -2- 

1 16 








21 


3| 


1 a 
x 4 


- 






2| 


3| 


I'll 
A 16 



TABLE IV 

Rough Square and Hexagon Nuts. U. S. Standard 

(franklin institute) 



Diameter 


Width of 


Thickness 


Diameter 


Width of 


Thickness 


of Bolt 


Nut 


of Nut 


, of Bolt 


Nut 


of Nut 


l 

4 


i 

2 


i 

4 


1 


1 5- 


1 


5 


19 


5 


H 


1 J- 3 - 
1 16 


11 


16 


32 


16 


3 

8 


11 

16 


3 

8 


U 


2 


H 


7 


25 


7 


U 


2-3- 
"16 


if 


16 


32 


16 


1 
2 


7 
8 


1 
2 


u 


"8 


H 


9 
16 


31 
32 


9 
16 


I 5 - 

x 8 


9-2- 
•^16 


1 5 

1 8 


5 

. 8 


lft 


5 

8 


I 3 - 


21 


I 1 
A 4 


3 

4 


H 


3 
4 


1* 


015 
*"16 


1 8 


7 
8 


1ft 


7 
8 


2 


31 


2 








21 


3i 


2i 


( 






2| 


3| 


2^ | 



lines CD. Points E are found by projecting from the plan view as 
indicated. 

In Fig. 28, the construction is similar. The points N are first 
found by projecting from the top and bottom of the circle in the 
plan view; then the lines NL are drawn, making angles of 30° with 
the line NN. (The proportions for the radii which are given, hold 
good only when the angle of 30° is used.) Next draw the construc- 
tion line LL and draw the arc tangent to it with a radius A equal 
to two and one-quarter times the diameter of the bolt, the same as 
in Fig. 27. To draw the chamfer in the other side view, draw the 



26 MACHINE DRAWING 

construction line parallel to and at a distance from CC equal to the 
distance LL from NN and draw the arcs tangent to this line with 
radius B equal to one-half of A. The lines EF are then drawn as 
explained for Fig. 27. 

Most of the bolts in common use are made standard sizes, that 
is, for a certain diameter of bolt there are a corresponding standard 
diameter and thickness for the head and the nut, and a standard 
number of threads per inch, so that if the bolt which the draftsman 
wishes to use has these standard dimensions they may be omitted 
from the drawing and a note made that the bolt is standard. Then 
the only dimensions necessary to be given are the diameter, the 
length under the head, and the length of the threaded part. 

Tables III and IV give the United States standard sizes of 
square and hexagonal heads and nuts for bolts. The columns 
headed "Width of Nut" and "Width of Head" give the shortest 
dimension of the square or hexagon, that is, the diameter of the 
inscribed circle, or the distance across flats. The standard number 
of threads per inch can be found from the table already given. 

Specifications for Pipes and Pipe Threads. Kinds of Pipe. 
The various kinds of pipe in common use are made to standard sizes, 
and as the draftsman very often comes in contact with piping we 
will consider it briefly. The kinds commonly used are wrought- 
iron or steel pipe, brass pipe made to the size of wrought-iron pipe, 
and cast-iron pipe. The cast-iron pipe is made of different weights 
and form, according to the purpose for which it is to be used. Stand- 
ard wrought-iron pipe is rated by its nominal inside diameter, 
although the actual diameter does not in most cases quite agree with 
the nominal diameter. For example, a J -inch pipe is a pipe, the 
hole in which is supposed to be J inch in diameter, but if measured 
it will be found to be nearly J of an inch larger. 

Standard Threads and Fittings. The threads on pipes and pipe 
fittings are also made to standard, and stock taps and dies made for 
the various sizes of pipe. These taps and dies are spoken of, or de- 
scribed, by stating the size of the pipe for which they are intended. 
For example, a J -inch pipe tap is a tap of the proper size, shape, 
and number of threads per inch to cut the thread in a hole to receive 
a J-inch pipe. Threaded holes are made tapering for pipes, the 
standard taper being } inch per foot, that is, the diameter of the 



MACHINE DRAWING 



27 



TABLE V 
Standard Sizes of Wrought=Iron Pipe 



Nominal Size 


Vs 


k 


% 


H 


% 


1 


1M 


1H 


2 


Actual Inside 
Diameter 


.27 


.364 


.494 


.623 


.824 


1.048 


1.38 


1.611 


2.067 


Outside 
Diameter 


.405 


.54 


.675 


.84 


1.05 


1.315 


1.66 


1.90 


2.375 


Nominal Size 


2V 2 


3 


2V2 


4 


4^ 


5 


6 


7 


8 


Actual Inside 
Diameter 


2.468 


3.067 


3.548 


4.026 


4.508 


5.045 


6.065 


7.023 


7.982 


Outside 
Diameter 


2.875 


3.50 


4.00 


4.50 


5.00 


5.563 


6.625 


7.625 


8.625 



TABLE VI 
Standard Threads for Wrought=Iron Pipe 



— ^— — — - — ^— — ^— — — — — 

Nominal 
Size of Pipe 


H 


H 


H 


H 


H 


1 


IX 


IK 


2 


Threads per 
Inch 


27 


18 


18 


14 


14 


ny 2 


nx 


uy 2 


UK 


Nominal 
Size of Pipe 


2V 2 


3 


sy 2 


4 


4^ 


5 


5V 2 


7 


8 


Threads per 
Inch 


8 


8 


8 


8 


. 8 


8 


8 


8 


8 




holes decreases at the rate of j inch per foot. In representing a hole 
which is threaded with a pipe tap, the hole is drawn of a diameter 
at its larger end about equal to the outside diameter of the pipe 
which is to be screwed into it, and 
is drawn tapering. It is well to make 
the taper considerably greater than 
the actual taper, so that the person 
looking at the drawing may see at a 
glance that the hole is for a pipe. 

The thread is indicated in one of 
the conventional ways previously explained, but the number of 
threads per inch and the diameter of the hole need not be given; 
instead, a note is made that the hole is tapped for a certain size 
pipe. Fig. 29 illustrates this. 

Tables V and VI which show the standards for wrought-iron 
pipe may be found convenient. 

Scale Drawings* When the object which is to be drawn is not 
so large but that it can be easily shown actual size (or full size as it 



Fig. 29. Conventional Drawing of 
Thread in a Pipe Fitting 



28 MACHINE DRAWING 

is called) on a sheet of paper of convenient dimensions, it is good 
practice to draw the piece full size. In many cases, however, the 
machine, or the building, or whatever is to be drawn, is so large 
that it would be impossible to draw it full size. Then the drawing 
is made to some reduced scale, that is, all the dimensions are drawn 
smaller than the actual dimensions of the object itself; all dimen- 
sions being reduced in the same proportion. For example, if a piece 
is to be drawn \ size, the distance from one point to another on the 
drawing would be \ what it is on the piece itself; if the drawing is 
\ size, the distance on the drawing would be \ what it is on the piece 
itself, and so on. In dimensioning such a drawing, the dimension 
which is written on the drawing is the actual dimension of the piece, 
and not the distance which is measured on the drawing. This fact 
must be very clearly understood by the student. 

Methods of Reducing Dimensions. The common method of 
reducing all the dimensions in the same proportion is to choose a 
certain distance and let that distance represent one foot, this dis- 
tance is then divided into twelve parts and each one of these parts 
represents an inch; then if half and quarter inches are required these 
twelfths are subdivided into halves, quarters, etc., until the sub- 
divisions become so small that they cannot be used. We now have 
a scale which represents the common foot rule with its subdivisions 
into inches and fractions; but our new foot is smaller than the ordi- 
nary distance which we call a foot, and of course its subdivisions are 
proportionately smaller. When we make a measurement on the 
drawing we make it with our reduced foot rule and when we make 
a measurement on the machine itself we make it with the common 
foot rule. 

Draftmen's Scales and Their Use. Draftsmen's scales can be 
bought which have different distances thus divided, so that if the 
draftsman wishes to draw a piece \ size he looks over his scale until 
he finds a distance of 3 inches (which is of course i of a foot) divided 
as explained above, and he uses this to measure with on his drawing. 
His drawing would then be made to a scale of 3 inches to the foot. 
In the same way, if he wishes to make his drawing jV s i ze ne finds 
on his scale 1 inch divided into twelfths and fractions of twelfths and 
uses this as his standard of measurement; if he wishes to make his 
drawing j-g size he uses a quarter inch with its subdivisions. 



MACHINE DRAWING 



29 



Sometimes if the piece to be drawn is too small to be satisfactorily 
shown full size, the drawing is made to an enlarged scale, such as 
twice size, three times size, etc. 

The mistake of choosing the wrong distance to use on a scale 
is often made. Fcr example, if one wishes to draw a piece J size, he 
may look over his scale for a place marked J, and use this for his 




■SMO/7T PR LEVEFf 
ONE STEEL FOFIG/NG 

Fig. 30. Reduced Scale Drawing. Actual Scale, 3"= 1' 

standard for \ size, which is wrong. The figure on the scale indicates 
the distance which is divided up to represent 1 foot, so that the 
part of the scale which has \ marked on it means that \ of an inch 
is divided up into twelfths, or in other words, if a drawing is made 
according to that scale it will be ■$-§ size. 



30 MACHINE DRAWING 

Usual Scales for Drawings. The best scales for shop drawings 
in the United States are those readily derived from the common foot 
rule, such as full size, 6 inches = 1 foot, 3 inches = 1 foot, 1J inches 
= 1 foot. These are the most common, most easily read from an 
ordinary scale, and one of these can usually be adopted. The 
.student should learn to read these from an ordinary scale without 
being confined to a special graduation. To do this it is not necessary 
to divide each dimension by 2, 4, and 8 to get | size, \ size, or J size, 
and then lay down the result. For § size, or 6 inches = 1 foot, 
| inch on an ordinary rule represents 1 inch. Hence, each \ inch 
may be read as 1 inch, and its subdivisions accordingly, thus: 

o 1 2 

For 3 inches = 1 foot, or \ size, \ inch represents 

±1 



12 3 4 

1 inch, and looks thus : , i , For \\ inches = 1 foot, or 



i 1 1 1 1 1 1 1 1 1 1 1 1 1 1 



\ size, | inch represents 1 inch, and looks thus: 



It is very easy to get accustomed to this, and it saves much time 
and trouble hunting up a special scale every time. 

The other allowable scales, less common, but sometimes neces- 
sary on large work, are 1 inch = 1 foot, \ inch = 1 foot, \ inch = 
1 foot, | inch = 1 foot, \ inch = 1 foot, and \ inch = 1 foot. To 
use these scales conveniently, special graduation is desirable. 

Every drawing should have the scale to which it is made plainly 
marked upon it, as a part of, or adjacent to, the title. 

Fig. 30 shows a detail which has been reduced in making the 
cut so that its dimensions are on a scale of 3 inches per foot, or \ 
size. By applying his scale to this cut and comparing the readings 
of his scale with the dimensions as given, the student will gain a 
clear understanding of a reduced scale drawing. None of the other 
cuts in this book are reduced for the purpose of scaling, hence have 
no even relation to their dimensions as given. 

GENERAL SYSTEM FOR SHOP DRAWINGS 

The principles of detail drawings having been thoroughly dis- 
cussed in the preceding pages, the general system to be followed in 
preparing shop drawings for the workman's use will now >be outlined 
and illustrated. 



MACHINE DRAWING 31 

DETAILS OF PREPARATION 

First Step — Sketches. As previously stated, for a new machine, 
the original sketches will be supplied by the designer, and it is the 
duty of the detail draftsman to read and interpret them; or the 
designer may furnish a rough general layout to scale, from which the 
detail draftsman must pick out the details, scaling off the dimen- 
sions. 

Oftentimes certain details of an existing machine have to be 
copied, in which case the sketches will have to be made by the detail 
draftsman himself, from the machine. Proficiency in the art of 
making sketches is a very valuable and necessary acquisition for any 
draftsman. Accuracy, completeness, clearness, and rapidity in mak- 
ing are the principal requirements for a good sketch. 

The sketches should be made so clear, that even if they are laid 
aside for a long time they can be readily understood without depend- 
ing at all upon memory. There is a strong tendency for the be- 
ginner to make his sketches hurriedly, thinking that when he comes 
to finish his drawing he can supply the details from memory. This 
is a bad plan and will lead to many mistakes. The sketches must 
be so clear and complete that anyone can read them who has never 
seen the machine. No attempt need be made to draw them to scale, 
but all dimensions, carefully measured from the machine, should 
be placed on the sketch. 

Second Step — Pencil Drawing. After the sketches are made, 
the next step is the making of the pencil drawing from the sketches, 
accurately to scale. The size of the plate on which the drawing is 
to be made is usually fixed by some standard. Where many draw- 
ings are made and kept in an office, it is desirable to keep the plates 
of uniform size, as far as possible. It is good practice to have two 
or three standard sizes of plates, one for small, one for medium, and 
one for large drawings. 

Assuming, then, that we have our paper tacked on the drawing 
board and the plate laid out, the next step will be to arrange the 
drawings of the various pieces on the plate so that there will be 
room for all and so that they may be properly placed with relation 
to each other. It may happen that there will not be room on one 
plate for all the pieces, but that two or more plates will be required. 
When the parts must be thus arranged on different plates, an effort 



32 MACHINE DRAWING 

should be made to keep on the same plate those parts which belong 
together. For example, if we were drawing a lathe, the details of 
the parts of the head stock might form one plate, the apron another, 
and so on. 

In locating the various pieces on a plate, they should be placed 
as nearly as possible in the same relative position to each other 
that they bear in the machine, except that they are separated. For 
example, if a nut belongs on the end of a screw, it is desirable to 
draw it on the same center line with the screw and at the end where 
it belongs. If a piece is vertical in the machine it should be vertical 
on the plate, and if horizontal in the machine, it should be horizontal 
on the plate. 

The approximate location of the pieces on the plate may be 
easily decided by taking a small sheet of paper of about the same 
proportion as the plate, but perhaps \ or \ size, and sketching on it 
roughly the outline of the various pieces. The arranging of the 
plate should not be allowed to take much time, but should be done 
as rapidly as possible. After the location of each view of each piece 
is determined, the pencil drawing should begin (to scale) with one 
of the principal pieces. In almost all cases a center line is first 
drawn. It is better to carry along all the views of a piece at once, 
instead of completing one view at a time. The piece started should 
have all its views finished and completely dimensioned before another 
piece is begun; exceptions to this are sometimes necessary for special 
reasons. The lines should be drawn accurately, but no attempt need 
be made to obtain finish; thus, in order to save time, the lines may be 
run past the point where they should properly stop, etc. Nothing 
should be omitted, however. 

Third Step — Tracing. Having finished the pencil drawing, the 
next step is the inking. In some offices the pencil drawing is made 
on a thin, tough paper, called bond paper, and the inking is done 
over the pencil drawing, in the manner with which the student is 
already familiar. It is more common to do the inking on thin, trans- 
parent cloth, called tracing cloth, which is prepared for the purpose. 
This tracing cloth is made of various kinds, the kind in ordinary use 
being what is known as "dull backs", that is, one side is finished 
and the other side is left dull. Either side may be used to draw 
upon, but most draftsmen prefer the dull side. 



MACHINE DRAWING 33 

The tracing cloth is stretched smoothly over the pencil drawing 
and a little powdered chalk rubbed over it with a dry cloth, to 
remove the slight amount of grease or oil from the surface and make it 
take the ink better. The dust must be carefully brushed or wiped off 
with a soft cloth, after the rubbing, or it will interfere with the inking.- 

The drawling is then made in ink on the tracing cloth, after 
the same general rules as for inking on paper, but care must be 
taken to draw the ink lines exactly over the pencil lines on the paper 
underneath, which should be heavy enough to be easily seen through 
the tracing cloth. The ink lines should be firm and heavy to assure 
good blue prints. In tracing, it is better to complete one view at 
a time, because if parts of several views are traced and the drawing 
left for a day or two, the cloth is liable to stretch and warp so that 
it will be difficult to complete the views and make the new lines fit 
those already drawn and at the same time conform to the pencil 
lines underneath. For this reason it is well, when possible, to com- 
plete a view before leaving the drawing for any length of time, al- 
though of course on views in which there is a good deal of w T ork 
this cannot always be done. In this case the draftsman must 
manipulate his tracing cloth and instruments to make the lines fit 
as best he can. A skillful draftsman will have no trouble from this 
source, but the beginner may at first find difficulty. 

Inking on tracing cloth will be found by the beginner to be 
quite different from inking on the paper to which he has been accus- 
tomed, and he will doubtless make many blots and become dis- 
couraged with his first attempt to make a tracing. After a little 
practice, however, he will find that the tracing cloth is very satis- 
factory and that a good drawing can be made on it quite as easily 
as on paper. 

The necessity for making erasures should be avoided, as far 
as possible, but when an erasure must be made a good ink rubber 
or typewriter eraser may be used. If the erased line is to- have 
ink placed on it, such as a line crossing, it is better to use a soft 
rubber eraser. All moisture should be kept from the cloth. 

Fourth Step — Blue Printing. The tracing, of course, cannot be 
sent into the shop for the workmen to use, as it would soon become 
soiled and in time destroyed, so that it is necessary to have some 
cheap and rapid means of making copies from it. These copies are 



34 MACHINE DRAWING 

made by the process of blue printing, in which the tracing is used in 
a manner similar to the use made of a negative in photography. 

Almost all drafting rooms have a frame for the purpose of 
making blue prints. These frames are made in many styles, some 
simple, some elaborate. A simple and efficient form is a flat sur- 
face usually of wood, covered with padding of soft material, such as 
felting. To this is hinged the cover, which consists of a frame 
similar to a picture frame, in which is set a piece of clear glass. The 
whole is either mounted on a track or on some sort of a swinging 
arm, so that it may readily be run in and out of a window. 

The print is made on paper prepared for the purpose by having 
one of its surfaces coated with chemicals which are sensitive to 
sunlight. This coated paper, or blue-print paper, as it is called, 
is laid on the padded surface of the frame with its coated side upper- 
most; the tracing is laid over it right side up, and the glass pressed 
down firmly and fastened in place. Springs are frequently used to 
keep the paper, tracing, etc. , against the glass. With some frames it is 
more convenient to turn them over and remove the backs. In such 
cases the tracing is laid against the glass, face down; the coated paper 
is then placed on it with the coated side against the tracing cloth. 

The sun is allowed to shine upon the drawing for a few minutes, 
then the blue-print paper is taken out and thoroughly washed in 
clean water for several minutes and hung up to dry. If the paper 
has been recently prepared and the exposure properly timed, the 
coated surface of the paper will now be of a clear, deep blue color, 
except where it was covered by the ink lines, where it will be per- 
fectly white. 

The action has been this: Before the paper was exposed to 
the light the coating was of a pale yellow color, and if it had then 
been put in water the coating would have all washed off, leaving 
the paper white. In other words, before being exposed to the sun- 
light the coating was soluble. The light penetrated the transparent 
tracing doth and acted upon the chemicals of the coating, changing 
their nature so that they became insoluble; that is, when put in 
water, the coating, instead of being washed off, merely turned blue. 
The light could not penetrate the ink with which the lines, figures, 
etc., were drawn, consequently the coating under these was not 
acted upon and it washed off when put in water, leaving a white 



MACHINE DRAWING 35 

copy of the ink drawing on a blue background. If running water 
cannot be used, the paper must be washed in a sufficient number of 
changes until the water is clear. It is a good plan to arrange a tank 
having an overflow, so that the water may remain at a depth of 
about 3 or 4 inches. 

The length of time to which a print should be exposed to the 
light depends upon the quality and freshness of the paper, the chem- 
icals used, and the brightness of the light. Some paper is prepared 
so that an exposure of one minute, or even less, in bright sunlight, 
will give a good print, and the time ranges from this to twenty 
minutes or more, according to the proportions of the various chem- 
cals in the coating. If the full strength of the sunlight does not 
strike the paper, as, for instance, if clouds partly cover the sun, the 
time of exposure must be lengthened. 

Blue-print paper should not be exposed to bright actinic light 
except during the process of printing. It is not, however, so sensi- 
tive as the ordinary dry plate and may be handled in a subdued 
light if the exposure is very brief. When not in use the paper 
must be kept in a dry, dark place and should be hermetically sealed. 

A more modern type of blue-print machine is the electric ma- 
chine, usually arranged in the form of a vertical cylinder of glass, 
around which is placed the sensitized paper and the tracing, and 
along the longitudinal axis of which travels an electric arc lamp 
at a uniform speed. This speed is so adjusted that the right ex- 
posure is given to the sensitized paper. There are several other 
types of electric blue-printing machines, all based upon the same 
idea of uniform exposure of the sensitized paper to the rays of one 
or more arc lamps. These machines are a positive necessity to 
modern drawing offices, because of the uncertainty of sunlight, and, 
therefore, limited capacity for turning out prints. With the electric 
machines there is no limit, and they may be run to their full capacity 
24 hours a day if desired. 

FORMULA FOR BLUE=PRINT SOLUTION 

Dissolve thoroughly and filter. 

A. Red prussiate of potash 2\ ounces 

Water 1 pint 

R Ammonium -citrate of iron 4 ounces 

D ' Water 1 pint 

Use equal parts of A and B. 



36 MACHINE DRAWING 



with 



FORMULA FOR BLACK PRINTS 
Negatives. White lines on blue ground; prepare the paper 

Ammonium-citrate of iron 40 grains 

Water 1 ounce 

After printing wash in water. 

Positives. Black lines on white ground; prepare the paper 

with: 

Iron perchloride 616 grains 

Oxalic acid 308 grains 

Water 14 ounces 

f Gallic acid 1 ounce 

Develop inj Citric acid 1 ounce 

[Alum 8 ounces 

Use 1 J ounces of developer to 1 gallon of water. Paper is fully 
exposed when it has changed from yellow to white. 

Assembly Drawings. We have followed through the process of 
making a detail drawing, from the sketches to the blue print ready 
for the workmen. Such a detail drawing or set of drawings shows 
the form and size of each piece, but does not show how the pieces 
go together and gives no idea of the machine as a whole. Conse- 
quently, a general drawing or assembly drawing must be made, 
which will show these things. Usually two or more views are neces- 
sary, the number depending upon the complexity of the machine. 
Very often a cross section through some part of the machine; chosen 
so as to give the best general idea with the least amount of work, 
will make the drawing clearer. 

The number of dimensions required on an assembly drawing 
depends largely upon the kind of machine. It is usually best to give 
the important over-all dimensions and the distance between the 
principal center lines. Care must be taken that the over-all dimen- 
sions agree with the sum of the dimensions of the various details. 
For example, suppose three pieces are bolted together, the thickness 
of the pieces, according to the detail drawing, being 1", 2" and 5§" 
respectively; the sum of these three dimensions is 8 J" and the dimen- 
sions from outside to outside on the assembly drawing, if given at 
all, must agree with this. These over-all dimensions serve as a 
check and relieve the mechanic of the necessity of adding frac- 
tions. 



MACHINE DRAWING 37 

ILLUSTRATIVE DRAWINGS 

The following illustrative drawings show the common practice 
in making working drawings, which it would be tedious and difficult 
to formulate as rules to guide the student. By a careful study of 
the illustrations, all of which are practical working drawings of a 
variety of pieces, and a close following of the description, more can 
be learned as to making a drawing than by adhering to a multitude 
of rules. After a study of the preceding pages, expounding the 
principles involved, the student will find most of his further ques- 
tions answered by reference to Figs. 31 to 50 inclusive. While he 
may find that the methods of lines and dimensions shown in these 
figures are in some ways different from those he may see or hear of 
from other quarters, he should remember that the language of 
drawing differs widely in usage. The result desired, however, is 
always the same, namely, complete instructions to the workman. This 
is the sole test of a good drawing, however made, and the student's 
aim should always be to satisfy this requirement. 

Crank — Rough Sketch. In making working drawings of a 
machine the detail draftsman must secure the several dimensions of 
the parts, either by measuring the general layout which has been 
made by the designing draftsman, or he may be given a rough sketch 
of the part, which he is to develop into an exact working shop draw- 
ing. Sometimes he may himself be called upon to go into the shop 
and measure up the parts of an existing machine, making his own 
sketches, and then detail drawings from them. Such sketches, while 
of the roughest kind, must be accurately and completely dimensioned 
at the time the sketch is made, as it is not always convenient or 
possible to make subsequent trips to the machine to fill in lacking 
dimensions on the sketch. The making of satisfactory sketches is 
not as easy as would at first appear, but is quite an art in itself, 
acquired by systematic action and experience. 

An illustration of a sketch of this kind is shown in Fig. 31, the 
subject being a crank, keyed and clamped to a shaft. The first 
thing to do is to sketch the piece roughly but with sufficient care to 
enable the dimensions to be put on. (A soft or medium pencil is the 
best for such purpose and any scrap of paper or a sketching pad will 
suffice.) Each portion of the piece should then be separately con- 



38 



MACHINE DRAWING 



sidered and carefully gone over to see that it is not only properly 
located but that it has the three dimensions, length, breadth, and 
thickness properly noted. 

Thus in Fig. 31, the large hub should first be located by giving 
its distance 10J " from the center of the smaller hub, then its diameter 
51" should be given, the distance between its faces 3|", and 6" radius 
between them; next, the diameter of the hole to receive the shaft 
2yf ", after which it is noted that it has a key way, the dimensions of 
which are necessary. Then the boss for the clamping bolt should 




»-A\^li| ITTT 



»lftt*m- 



Fig. 31. Preliminary Sketch of Crank 



be located by the figure 2 J " to its center, its location in the other 
direction being on the center line of the arm. This boss has a 
diameter of 2f " and a length of 2|" each side of the center to the 
finished surface, the depth of the counterbore being tV"> an d the 
width of the slot to the bore \", all of which dimensions should be 
carefully put on. The boss has a hole in it tapped at one end for a 
1" bolt and drilled at the other end 1^"- This completes the figur- 
ing of the large hub and we can proceed to dimension the other end 
of the arm. This has a diameter of 4f ", the thickness of the arm 
being 2", and there are facing pads on either side \" high, bringing 



MACHINE DRAWING 39 

the total distance from face to face 2J"; in order to show positively 
that these portions are central with the faces of the large hub, the 
figure ¥ is put at one side; the diameter of these facing pads is 3J", 
and the hole through the head of the crank is 1 \ |" diameter. Having 
put on the above figures we now have to provide a connection be- 
tween the head of the crank and the hub, and it therefore becomes 
necessary to give figures, for the size of the arm; the thickness of the 
arm has been already given as 2", and the width being the same as 
the diameter of the hub, the side lines are simply drawn tangent to 
the same; at the smaller end the width may be conveniently given 
along a line tangent to the facing pad as 3f ". The arm is filleted 
into the hub by 1" radius. The only thing now uncertain is whether 
the corners of the arm are sharp or rounded, and this is shown by 
the little section of the corner giving \" radius. 

The above description is tedious and the dimensions can prob- 
ably be put on more quickly than the discussion of them can be 
read, but it should be especially noted that the systematic method 
has been followed of taking each part of the piece separately and 
dimensioning it before taking up any other part. While this is 
not always entirely possible to do in complicated pieces, yet it is 
absolutely necessary that in general this principle be always fol- 
lowed; otherwise it is impossible to be sure that all dimensions are 
on. 

The description above also applies to the dimensioning of the 
piece after it is drawn in detail, this being represented in Fig. 32. 

Referring to this figure, the bold character of the drawing should 
be noted, the solid lines being strong and of absolutely different 
character from the center or dimension lines. There is no uncer- 
tainty about the direction or termination of the lines; the figures are 
bold, plainly made, and absolutely clear; there can be no possible 
excuse for the workman to read any of the lines or dimensions 
wrongly. In other words, the drawing satisfies the definition of 
a working drawing, as previously given, in that it conveys absolutely 
definite instructions to the icorkman, expressed in the simplest and 
most straightforward way. 

Finished Drawing. On most machine parts a portion only of 
the surfaces are finished; and these are usually indicated, as previ- 
ously noted, by the small letter / placed across the line representing 



40 



MACHINE DRAWING 



the surface; this indicates to the pattern maker that he is to allow 
extra stock on the pattern, so that when the rough casting is made 
there will be sufficient metal to enable the finishing cut to be taken 
to the proper dimension. These finished surfaces are the most 
important surfaces of the piece, to which all the other parts have 
to be related. In order that the several parts of the machine may 
properly go together, it is necessary for the draftsman, in putting 
on the figures, to start from some one finished surface, and so arrange 




C'BORE 



Fig. 32. Detail Drawing of Crank 

the figures that the machinist can readily work from one finished 
surface to another. In Fig. 32 the dimensions of the rough parts 
as given may not be exactly maintained in the casting, but the 
distances between the finished surfaces must be exactly secured. 
The method of figuring a keyway is illustrated in this figure, and it 
should be carefully noted that the depth of the keyway (A") is given 
from the corner where the side of the keyway intersects the bore; 
this is because the depth of the keyway is readily measured by scale 
from this point. 

The thread for the 1" bolt is indicated in this case by a double 
line, the inside line representing the bottom, the outside representing 



MACHINE DRAWING 



41 



the top of the thread, while the lines of the helix are entirely omitted. 
This is not as common a method of representing a thread as the 
conventional method previously described. 

Bell Crank. Fig. 33 shows a bell crank fastened to its shaft by 
means of a set screw, the same general features being noted in this 
as in the preceding figure. A further point is the method of express- 
ing the distance between the faces of the principal hub and the 
smaller hub, "10" less - 6 V "• This method of stating a dimension is 
quite common among certain manufacturers, as it saves giving odd 
dimensions and conveys more quickly to the workman's mind what 




BELL CRANK 

ONE- G.I . 

Fig. 33. Method of Showing Dimensions on Detail Drawing 

the dimension is. The other method of stating this would be "9 ff " ", 
which is obviously a somewhat cumbersome and odd dimension; it 
is easier for the machinist to read 10" on his scale and finish the 
distance ^ " less, than it is to use the actual figure. This point is an 
instance in which the instructions furnished by the drawing to the 
workman are simplified for his benefit. 

Another point worth noting in this figure is that circles are 
dimensioned by giving the diameters in preference to the radii; this 
is for the benefit of the pattern maker and the machinist, who always 
use calipers for measuring these parts. When the radii are given, 
the workman is forced to multiply the radius by two in order to 
secure the dimension for his calipers; and it is always better to 



42 



MACHINE DRAWING 



remove the chance of error on the part of the workman in the shop 
when making mathematical calculations. A detailed drawing should 
be so completely dimensioned that there will be no occasion for the 
workman to make any calculations himself; for, even if he is com- 
petent to do it, the responsibility for the correctness of the figures 
should be on the draftsman. In practically all shops the workmen 
are not allowed to scale the drawings in case dimensions are lacking, 
but are required to go to the drafting room and have further dimen- 
sions put on as required. A good detail drawing should require no 
such additions. 




ROCKER ARM PIN 
ONE- CMS. 

Fig. 34. Detail of Rocker Arm and Pin 

Rocker Arm and Pin. Fig. 34 shows the detail of a rocker arm 
and pin, such as are frequently found in connection with the valve 
gear of a steam engine. This is a case where it is just as clear to 
detail two pieces together as to separate them entirely, the rocker 
arm pin being shown in position in the large hub and dimensioned in 
that position. This is not only simpler, but it gives the added 
information to the workman of just how the pin goes in the arm, 
and enables him to make his fits accordingly. 



MACHINE DRAWING 43 

This principle of detailing several pieces together may, however, 
be carried to the point where the drawing becomes confused and 
complicated; then it is best to separate the detail of the parts. 
There are often special reasons requiring the detailing of parts of 
one kind on one sheet and of another kind on another sheet; for 
example, some shops detail forgings on one sheet, castings on 
another, parts to be made on the screw machine on another, and 
turret lathe work on another, etc. Such arrangements are, however, 
dependent upon the particular shop organization to which they 
apply. 

Link Stud. Fig. 35 shows a link stud, also used in connection 
with the valve gear of an engine. On such pieces as this it is usually 
considered that they are finished all over unless otherwise mentioned. 
It is always desirable, in finished 
pieces of this character, to give T - 
the length over-all of the pieces, V 



2 ACROSS FLATS 



L 



JiL- 



i 



■*r- 



'P 



in order that the workman may 

quickly determine how much t fi 

stock to order from the stock 

room without having to add up LINK STUD 

^ £ u * +i, • TWO-STEEL 

the figures between the various 

° . Fig. 35. Detail Drawing of Link Stud 

shoulders of the piece. The head 

of this stud is a hexagon, and the usual method of calling for the 
hexagon is given in the note, "2" across flats". The reason the dis- 
tance across flats is specified is to enable the workman to see at once 
what the necessary width of the jaws of the wrench must be in 
order to fit the head of the stud. 

Flange Coupling. Fig. 36 shows a flange coupling such as 
would be used to connect up a line shaft in a shop, or any heavy 
machinery shafting. The detail construction of this is most clearly 
shown by making the drawing in cross section. This drawing is a 
good illustration of the placing of the dimensions entirely outside 
the lines of the drawing, thus enabling any changes to be made in 
the figures without in any way obliterating the drawing. It also 
keeps both drawing and figures definite and clear, avoiding any 
possibility of confusion. Each half of the coupling is fastened to its 
shaft by a tapered key; and in order that it may be clearly under- 
stood which way the top of the keyway is tapered, the arrows, 



44 



MACHINE DRAWING 



shown in the cross-sectional view, indicate the direction in which 
the key is driven home. 

Pattern Numbers. On this drawing are indicated the pattern 
numbers. They would be equally necessary on all other castings 
illustrated in this book; but for purposes of simplicity they have 
generally been omitted. Pattern numbers are necessary, not only 
that the patterns may be filed away systematically, and readily 
found when wanted, but also that the necessary orders for the cast- 
ings may be written, and that the pieces may be identified on the 
drawings. For wrought-iron and steel pieces which have no patterns, 



MSC6 




2,£ Flange Coupling - Steel Casting 
2 - Female - MSC 6. Shp v/ifh shaft MS/ 7. 
2- Mole - MSCS. . - »' MS/8. 

Fig. 36. Detail Drawing of a Coupling, Using a Cross-Sectional View 



certain letters or numbers are given them, such that the identifica- 
tion is as complete as with castings. Castings, whenever possible, 
carry on their surface the pattern numbers in raised figures, and 
when received in the shop or field can thus be identified for assem- 
bling in the machine. Wrought-iron and steel pieces, which cannot 
have such figures raised upon them, are usually marked with painted 
letters and figures, to correspond with piece marks called for on the 
drawing, thus enabling them to be properly identified at the shop 
and in the field. There are many different systems in vogue for 
this numbering, dependent upon the particular requirements of the 
shop organization to which it applies. 



MACHINE DRAWING 



45 



Clamp Eye* Fig. 37 shows a piece designed to receive a threaded 
rod at one end and to clamp rigidly to a shaft by means of a bolt at 
the other. This detail, simple as it appears, is awkward to make, 
on account of the bolt boss being at an angle with the principal 
center lines. The lower view is a cross section, because, if the 
ordinary elevation were shown, it would have a series of ellipses 
showing the bolt boss projections. It is always desirable to avoid 
oblique projections of circular shapes on account of the difficulty of 
drawing same; moreover, the ellipses produced do not show the 




sTAP 



s» TO POINT 

— 'a 



Fig. 37. Detail Drawing with a Projection Thrown Off at an 
Angle with the Principal Center Lines 



construction as plainly as a straight projection. The method 
adopted in such cases is to throw off a straight projection at the 
same angle as the part in question makes with the principal center 
lines. In the present instance it is necessary to show that the boss 
for the bolt is f " radius, and that the boss is centrally located with 
the hub, which is readily done by the straight projection thrown off. 
In the cross-sectional view, the lines representing the thread appear 
to the eye sloped in the wrong direction, or as though the thread 
were left-hand. A moment's thought, however, will convince the 
student that, since the section taken is through the middle of the 
hole, we are merely looking at the back side of the hole, and that 
the threads of a right handed screw on the back side must neces- 
sarily slope in the direction as shown. In the case of the thread on 



46 



MACHINE DRAWING 



the bolt for the clamping hub, shown dotted, the lines of the thread 
appear right-handed to the eye, it being universal practice in the 
case of dotted threads to show the side only next the eye. If the 
threads on the back side of the bolt were also shown, they would 
slope in the other direction, crossing the other lines, and to draw 
them in would obviously cause confusion. 

Connecting Rod. Fig. 38 shows the connecting rod for a small 
steam engine. This piece calls for little comment. The outlines of 
the crank pin and cross-head pin are shown in dot-and-dash circles, 
and the relation of these centers to the rod is given. This is of some 
importance in enabling the detail of the boxes, which go in the heads 
of the connecting rod, to be correctly detailed and checked. It 




CONNECTING HOD 
^ ONT-sT£eL 

Fig. 38. Detail of a Connecting Rod 



should be carefully noted by the student, that any such information 
which can be given on the details, without confusing the drawing, 
to tie up one detail with another, is usually* good practice. It not 
only saves time in the drafting room in checking and general refer- 
ence work, but it gives the workman a better idea of how the parts 
are expected to go together, thus fulfilling the general definition of 
a working drawing as "complete and definite instruction". 

Gear with Split Hub. Conventional Drawing. Fig. 39 shows a 
gear with a split hub, the bolts through the hub being for the pur- 
pose of tightly clamping same to the shaft. This is an illustration 
of the conventional method of showing a gear with standard propor- 
tions of teeth. If the drawing were made exactly as the gear would 
look, it would be necessary to spend a large amount of time inking 
in the outlines of the 72 teeth around the circumference of the gear; 



MACHINE DRAWING 



47 



instead of doing this, the pitch line of the gear is shown, and circles 
drawn indicating the top and bottom of the teeth. The pitch 
diameter and outside diameter are given, and the proper depth of 
tooth cut to be made by the gear cutter; nothing more is necessary. 




GEAR 
CUT 73T.-LD.R INVOLUTE 
ONE- C. A 

Fig. 39. Detail of Gear with Split Hub 



The information which enables the workman to choose the proper 
cutter is given in the title; thus, "Cut 72 Teeth — 1 Diametral Pitch 
— Involute." The workman will receive' from the tool room a stand- 
ard involute cutter marked for 72 teeth, 1 diametral pitch. After 
placing same on the arbor of the gear-cutting machine, he will drop 
the cutter into the gear blank to the depth called for by the drawing; 



4* 



MACHINE DRAWING 



& this is accurately done, it will give the desired standard thickness 
and-clearance of the teeth, and the automatic indexing of the machine 
will produce the 72 teeth, accurately spaced. If the gear were a 
cast gear: — an which case the pattern maker would have to lay out 
the teeth and finish them one by one on the pattern — it would be 
necessary to draw one or two teeth on the circumference of the gear, 




Fig. 40. Detail of Gear with Solid Hub 



and give sufficient figures to enable him to lay out the teeth either 
by his dividers or by a template. In neither case, however, should 
the detail draftsman take the time to draw the teeth in any great 
number around the circumference of the gear; this is a very common 
thing for the young draftsman to do, and nothing shows his green- 
ness more. He should bear in mind that when the proper instruction 
has been conveyed by his drawing, any more time spent on it is 
wasteful. 

Cross Section. The cross section of the gear is shown to enable 
the necessary figures to be placed upon the rim and hub. In the 



MACHINE DRAWING 



49 



right-hand view, only one-half the complete circle of the gear is 
shown ; nothing would be gained by showing the other half, therefore 
it would be a waste of time and space on the drawing to make it. 

Attention is called to the method of indicating the dimensions 
of the arms, the breadth and thickness of the oval being indicated 
as follows: "6f" X 21""; this is a "short cut" which will usually 
answer, but it does not actually show the section of the arm. It 
would be better actually to make a cross section, as shown in the 
lower portion of the right-hand view, giving the actual radii for the 
section, as otherwise the pattern maker might make an arm more 
or less blunt on the ends than the draftsman intended. 

Spur Gear. Fig. 40 shows the detail of a spur gear with a T= 
shape arm. The gear drives through fitted bolts in the flange 
about the hub. Two or three teeth are dotted in, to show their 
dimensions, which are according to the standard involute system. 

Pinion for Spur Gear. 
Fig. 41 shows the detail of 
a pinion designed to mesh 
with the gear in Fig. 40, 
one view being sufficient. 

Pair of Beveled Gears. 
Fig. 42 shows the detail 
drawing of a pair of bevel 
gears. By careful study of 
this drawing, the student 
will gain an idea of the dimensions to be shown on a bevel gear. 

The gear-cutting machines, on which the teeth of these gears 
are cut, require the angles as given for the setting of the cutters, 
It should also be remembered that the casting must be finished by 
the machinist before the teeth are cut; hence the dimensions for 
hubs, diameters, etc., must be so put on that they can be conveni- 
ently used by the machinist in turning up the gear blank in an 
ordinary lathe. 

Worm and Worm Gear. Fig. 43 shows the detail of a worm 
and worm gear. The teeth on the worm gear are twisted; and if it 
were attempted to show their true projection, it would be a compli- 
cated and difficult piece of work. The worm gear is shown, there- 
fore, by drawing the pitch line of the teeth and other circles at the 




ONE-STEEL -F.A.O. 



Fig. 41. Detail of Pinion to Mesh with Gear of Fig. 40 



50 



MACHINE DRAWING 




rrr 


C5 


- 


^ 


i # 


CO 


u; 


IR, L, 


^ 


i 


if' 


3 


S 


3 


^ 




K 

to 


1 






V ^ 


:^ 


1 u 

Z2 


o>l>o 



52 



MACHINE DRAWING 



top and bottom of the teeth. At the point where the gear is in 
mesh with the worm, a portion of the rim is broken away, and the 
middle section shown. The worm threads, which are lines in the 
form of helices, are shown in the drawing merely by straight lines, 
this being the conventional way for representations of this character. 
Another way of showing the worm would be in cross section, in 
which case the. helical lines would be wholly avoided; as drawn, 
however, it has the advantage of at once conveying to the eye that 
it is a right-handed thread. 

T 




CYLINDER HEAD 
ONE- C.J. 

Fig. 44. Detail of Cylinder Head of Steam Engine 

Cylinder Head. Fig. 44 shows the cylinder head of a steam 
engine. Although in the drawing the entire circle is shown, it would 
have been just as clear if only one-half had been shown, similar to 
the manner of showing the side views of the gears just discussed. In 
the plan view, it should be noted that the tapped holes are indicated 
by double circles, while the drilled holes show a single circle. The 
inner circle for the tapped holes is intended to represent the bottom 
of the thread, while the outer circle represents the top of the thread. 
Another conventional method for a tapped hole is to fill in the circle 
entirely with black ink; the method illustrated, however, is the 
most common. 



MACHINE DRAWING 



53 



Water Cylinder for Triplex Pump. Fig. 45 shows a water 
cylinder for a triplex pump, and is an excellent illustration of many 
of the points heretofore brought out, combined on a single drawing. 
This drawing should be carefully studied in detail. Note the general 
boldness of the lines, and the sharp contrast between the full-line 
work and the center, dimension, and dotted lines. Note that in the 




Fig. 45. Detail of Water Cylinder for Triplex Pump 



cross-sectional views the dotted lines have been almost entirely 
eliminated, thereby leaving the section work clear and plain. There 
is no necessity of showing parts in dotted lines which are beyond 
the plane of the section, but in several places just enough simple 
dotted work is shown to convey the relation of the parts. 

Object of Each View. Each sectional view is made for a spe- 
cific purpose, and that purpose is never allowed to be obscured. 
The top plan is mainly to show the upper portion of the water cyl- 



54 MACHINE DRAWING 

inder; the cross section below it gives the principal interior view; 
the right-hand half-elevation and cross section are for the purpose 
of showing the face of the valve chamber and the interior of the 
valve chamber; the horizontal cross section in the upper right-hand 
corner of the drawing shows not only the interior of the barrel and 
valve chamber at two different points, but also a clear outline of 
the base of the entire casting. Each view must be used with the 
other to get a clear idea of the construction; but each view is so 
simple in itself that no confusion arises in the mind as to what its 
lines mean; one view is readily associated with the other, and the 
grouping of the four views is such that the eye passes easily over all 
of them. 

Method of Grouping Dimensions. Note the grouping of the 
dimensions, following in general the purposes of each of the views as 
explained above. On the top plan are given the dimensions affecting 
the top of the casting only. On the principal vertical cross section 
are given the greater part of the dimensions for the entire piece. 
This is as it should be, for the dimensions should always be grouped 
as much as possible on the principal view of an object, provided they 
can be clearly put on that view and not become so numerous as to 
cause confusion. A drawing over which the eye has to wander 
widely in search of the several dimensions of the same portion, is 
slow and difficult to read. On the right-hand half-elevation and 
cross section are the figures for the outline of the face of the valve 
chamber, and the location of the tapped holes for the hand-hole 
cover-bolts. On the horizontal cross section are given the figures for 
the interior dimensions of the valve chamber, and a complete dimen- 
sioning of the base of the casting. The special attention of the 
student is called to this systematic grouping of the dimensions on 
the view which will most clearly show them. A glance at this draw- 
ing is sufficient to suggest what a confusion of figures there would 
have been, had it been attempted to place them all on two views, 
and if, instead of cross sections, full and dotted lines had been used. 

Method of Showing Finished Surfaces. On this drawing is 
indicated a new method of showing finished surfaces. Each surface 
which is intended to be finished in the machine shop, has drawn next 
to it a medium-weight line consisting of a long dash and two dots. 
This method of showing finished surfaces is not as common as the 



MACHINE DRAWING 55 

one heretofore used, of writing the letter / across the line; it has the 
advantage, however, of conveying an absolutely definite idea of the 
extent of the surface to be finished, and in some instances is especially 
valuable on this account. It is a good way of specifying the finish ; 
but for general practice the letter / is simpler and perhaps more 
readily and universally understood. 

Analysis of Drawing. This drawing, while not complicated, 
contains quite a large number of dimensions, and is a good example 
of the principle of systematic figuring. " The student's attention, 
therefore, is called to the following analysis of the dimensions on the 
drawing. 

The casting consists of a barrel, in which the plunger slides, 
with a stuffing box at the top and a waterway at the bottom leading 
into the valve chamber; attached to this barrel is the valve chamber, 
consisting of two compartments, the lower one for suction, the upper 
one for discharge; to support both barrel and valve chamber and 
permit of their being bolted to the water-supply casting, a rectangu- 
lar base is provided. 

Beginning at the top of the casting, the figures for the stuffing 
box, inside and outside dimensions and thicknesses are given, and 
note made that the outline is square. The tapped holes for the 
gland studs, and bosses for the drips, are shown most clearly in the 
top plan, and are therefore dimensioned there. Next we come 
to the bore of the barrel to receive the plunger, and here the square 
shape of the casting changes to a round, the diameter and thickness 
of metal being given. Below this cylindrical part is the waterway, 
the height of which (2 J") is given, and then the 1" thickness of the 
base below. This completes practically all the dimensions of the 
barrel and stuffing box. 

Passing to the valve chamber, it is first necessary to locate the 
center line of same in reference to the barrel (10f" centers). This 
being done, the arrangement of valves is dimensioned, and figures 
given for the valve chambers, thus — length, breadth, depth, thick- 
ness of metal, fillets, etc. ; then follow the location of the face of the 
valve chamber, 5f" from the center line, and the layout for the hand- 
hole cover; then the location of the upper face of the valve chamber, 
14J" from the base, and the layout for the flange of the discharge 
pipe, which is shown on the top plan. 



56 MACHINE DRAWING 

Few figures as yet have been placed on the base of the water 
cylinder ; these are now completed by starting at one side of the base 
and going completely around same, giving not only external dimen- 
sions and radii, but also location of bolt-holes and their sizes — all 
of which are shown in the horizontal section. 

This completes the dimensions; and if the student has carefully 
adhered to each particular part of the casting until completely 
dimensioned, and has not passed in haphazard fashion from one 
portion of the casting to another, he will have succeeded in dimen- 
sioning the piece with absolute completeness. No part will have 
escaped being dimensioned, and no part will be dimensioned twice. 
It would be a good plan for the student to copy this drawing, using 
a scale of 3 inches to the foot, and, in making the drawing, to follow 
the description as given above in reading the figures from the cut. 
He will thus more clearly realize the systematic progress from one 
part of the casting to the other, and will himself check the figures 
shown. 

Hoisting Drum. Fig. 46 shows the detail of a hoisting drum to 
carry wire rope. Attention is called in this detail to the enlarged 
cross section of the rim, conveniently placed to show clearly the style 
of the groove. It should also be noted, that, instead of drawing the 
grooves the entire length of the drum, but a few are drawn at each 
end of the drum and a note placed against same to indicate that the 
grooves are to be cut the entire length. This is another "short cut" 
consistent with the definition of a working drawing. The breaking 
away of a portion of a view is illustrated in the right-hand elevation, 
in which a small section is exposed to show the method of fastening 
the end of the wire rope. 

Crane Drum Grooved for Chain. Fig. 47 shows a crane drum, 
grooved for chain, and carrying its driving gear and shaft. This is 
a very good illustration of the economy of grouping parts together, 
instead of detailing them separately. It is obvious that the drawing 
of each detail is just as clear as though it were separately drawn. In 
fact, the information conveyed is the most complete possible; for 
not only are the figures for each part clearly shown, but the exact 
manner in which the parts go together, thus enabling the workman 
to understand at a glance the assembling of the parts, and to make 
his fits accordingly. A general drawing for this purpose alone has 



MACHINE DRAWING 



57 




MACHINE DRAWING 



59 



to be made in the case of a complicated machine; and it would be 
confusing to put on such a drawing figures sufficient to detail each 
part. The draftsman who can properly judge when to use assem- 
bled drawings for detail dimensions, and when to avoid such use, 
will save a large amount of time and money in the production of 
drawings for shop use. A common rule that "every part shall be 
detailed separately" is in vogue in many drafting rooms; but it is 
seldom followed literally, and when so followed becomes a drag on 
office efficiency. A better rule is — "Detail every part separately 
when groups of parts cannot be clearly detailed together." 

Note on this drawing the method of indicating, by light diagonal 
lines across the shaft, the location of the bearings; also the enlarged 
view of a few teeth of the gears, with sufficient figures for the pattern 
maker to work out the teeth. These gears are "half-shrouded", or 
strengthened by a rim extending up to the pitch line. 



BEARING 




SHAFT 



ONE- STEEL- F.A.O . 
Fig. 48. Detail of an Ordinary Shaft 



Detail of Ordinary Shaft. Fig. 48 shows the detail of an ordi- 
nary shaft with a number of different bearings and fits upon it. It 
illustrates most of the common points which are necessary to be 
specified on shaft details. The distance, shoulder to shoulder, is 
usually given throughout the entire length of the shaft, and these 
distances summed up for the "over-all" dimension. The "over-all" 
dimension is important, because from it the stock is ordered and cut 
off; and the workman should not be required to add up a lot of 
figures to secure it. Fillets should be allowed at every shoulder, 
if possible, and their radius specified; in this way there is less liability 
to the formation of incipient cracks than if the corners are left sharp. 
Keyways should be carefully dimensioned and located. Bearings 
should be indicated by light lines running across the shaft diagon- 



60 MACHINE DRAWING 

ally; and it is good practice to print the name of each piece to which 
the shaft is fitted, just above the shaft at the point where such fit 
occurs, or the parts themselves are partially shown in light lines, as 
at A and B in the figure, thus enabling the workman to make the 
fits more intelligently. It is common practice to make all holes 
which receive shafts of exactly "gauge diameter", and to make the 
allowance for the fit in the shaft. For example, a "3" running fit" 
would mean that the hole in the piece to receive the shaft would be 
exactly 3" in diameter, while the shaft would be, say, "3" less .003'"'. 
Sometimes this allowance is indicated by giving the actual number 
of thousandths of an inch under size, as noted ; sometimes by calling 
for a "running fit", or a "wringing fit", or a "pressed fit", or a 
"drive fit", or a "tight fit", as desired. 

"Broken" Pieces and "Out=of=Scale" Dimensions. Shafts are 
often so long that it is difficult to represent their entire length on 
the sheet to the scale chosen. They are then "broken", as shown in 
the figure, and crowded up to a shorter length, the dimensions being 
depended upon to give the proper relation of the parts. 

When there is occasion, because of some change, to alter a 
dimension on a finished drawing, it is usually permissable to change 
the dimensions without rubbing out the lines of the drawing, pro- 
vided that no considerable number of other dimensions are affected, 
and provided that some sign or note is made on the drawing, calling 
attention to the fact that the dimension has been changed and that 
the drawing is "out of scale". Sometimes the dimension is placed 
in a circle thus © or a line drawn beneath it thus, &' ; or the 
words "out of scale" placed after it thus, *" (out of scale). Although 
workmen are not allowed to "scale" drawings, yet it is dangerous 
to have dimensions which are out of scale on the drawings unless 
special attention is called to that fact. 

The above remarks on "broken" pieces and "out-of-scale" 
dimensions are equally applicable to all details as to shafts, the 
points merely being illustrated by the figure under discussion. 

Bearing Stand with Cap and Boxes Removed. Fig. 49 shows a 
bearing stand with the cap and boxes removed. There is little of 
special note to discuss in regard to this, beyond calling attention to 
the general nature and type of the piece illustrated. The design is 
characteristic of pedestals and bearings found about stationary 



MACHINE DRAWING 



61 



engines of large size. Such parts are usually massive and heavy in 
their proportions, with well-rounded corners and smooth outline. 
The closed-box form of casting affords maximum strength with good 
distribution of material, and at the same time conveys to the eye the 
effect of a solid piece throughout. 



// tap- 



\-'°!r-\—ior^\ 




i DRILL 

Zs" LEVELING" 
SCREWS 



l§DRILL%?~ 

u 




BEARING STAND x 
OfiE-C.l. 



Fig. 49. Detail of Bearing Stand with Cap and Boxes Removed 



Sample Letters. Fig. 50 shows a sample sheet of plain letters, 
such as are particularly applicable to working drawings. They are 
especially devised for easy, quick, and uniform strokes. Each 
draftsman has a character of his own in lettering and figuring, and 
the form of lettering which is most natural for him to use is the one 



62 MACHINE DRAWING 

he will use to best advantage. It is necessary, however, to confine 
draftsmen to a general type in order to make their work reasonably 
uniform; and the sample sheet (Fig. 50) represents not only the most 
common type in use, but a type to which almost any draftsman 
can readily train his eye and hand. Whether the slopes are forward 

Small Letters 

, i it / 12 1 23 
12 I 2 12 1 2 t /„ 12 > 2 / 23 4 12 / 2 /B3 

:nn , pp. nrtrt;x . It" , uij-y\/ , w v/v , x/\ , i/t.f ■? 
abcdefahiiklmnoparstuvvvxYZ. 

CAPITAL LETTERS. 

A/AHt^ t'i l)t\ h ffyf fit Li H i Jj'KJK , j , M, 

M t ){\ p/£ # Hf'A v s T. ittlv.W.X.Y 7-fc~ 

ABCDEFGHIJKLMNOPQRSTUVWXYZ& 

t?X4Sfi7fiS*r> hkiiikhi 1234567890. 

ABCDEFGHIOKLMNOPQRSTUVNNXYZ &. 

Fig. 50. Sample Sheet of Plain Letters Used in Working Drawings 

or backward, or straight up and down, is of little importance, as long 
as the general style is maintained. 

Drawing Room Practice. Every drafting room has certain 
methods and rules peculiar to its own organization and that of the 
shop to which it supplies drawings. While it is impossible to formu- 
late any set of instructions which will cover all situations, the accom- 
panying sheet, "Drawing Room Practice," is consistent with general 
practice in modern drawing offices and the fundamental principles 
discussed elsewhere in this book. It is a condensed code of pro- 
cedure which the student will do well to hang in some convenient 
location near his table, and to consult freely as he works. It should 
not take the place of the explicit discussions of the text, but should 
be used as an index to it and as a reminder. 



MACHINE DRAWING 



63 



CHICAGO 



DRAWING ROOM PRACTICE: 

AMERICAN SCHOOL OF CORRESPONDENCE: 



ILLINOIS 



STD.SIZES 
PLATES 

DRAWNGS 

MARGINS 
SCALES 



TRIMMING 
SIZE 



(9"*12" I"x2" 

\l2"xl8" F*2" 

r ld"x24" 2fx4" 
24"* 36" Z?x4" 
ALLMARGINS fwiDE 
USE THESE SCALES IN 
PREFERENCE TO OTHERS 
12?= f FULL SIZE 
6"=!' HALF » 
3"= I' QUARTER n 
if- I' EIGHTH » 



PROJECTION 



DOTTED 
LINES 

PENCIL 
WORK 

TR. CLOTH, 
\CHARACTER 
OF 
LINES 



COLOR 
FIGURES 

DIMENSIONS 

ALLOWABLL 
ERROR 

NOTES 



THOUGHT 



TITLE 
FRAME 



CYLINDER 

FOR 



12x36 CORLISS ENGINE 



AMERICAN SCHOOL "CORRESPONDENCE 



CHICAGO 



ILLINOIS 



SCALE 3= 1' JULY 7J9/3. 



C.JC.&. 



{SAMPLE TITLE) 



CHOOSE LARGEST SCALE CONSISTENT WITH SIZE OF SHEET. 
USE SIMPLE PROJECTIONS ONLY. 

MARE VIEWS TO COMPLETELY ILLUSTRATE. NO MORE- NO LESS! 
PLACE VIEWS ON SHEET IN SAME POSITION AS PIECE OCCUPIES- 

IN ASSEMBLED MACHINE. 
WORK ALL VIEWS TOGETHER. DO NOT TRY TO FINISH ONE VIEW 

BEFORE BEGINNING ANOTHER. 
USE FEW DOTTED LINES ONLY WHEN ABSOLUTELY NECESSARY. 
USE CROSS SECTIONS FREELY IN PREFERENCE TO DOTTED LINES. 
MAKE PENCIL DRAWING SHARP AND DEFINITE, ABSOLUTELY 

COMPLETE j AND CHECH CAREFULLY BEFORE TRACING. 
USE ROUGH SIDE OF TRACING CLOTH TO PREVENT CURLING. 
LINES FOR SIMPLE LARGE SCALE DETAILS THUS'. 

» *» COMPLICATED SMALL » >' — 

» DOTTED >' 

» CENT£R 0ff ^ ML {daSHAND DOT » x 
» DIMENSION m m ■///////// » ^ 

» CROSS SECTION £ TO / ' APART ||§§|; 
USE BLACK INK FOR ALL LINES 

MAKE FIGURES BROAD, BOLD AND ABSOLUTELY CLEAR. 
MAKE ALL FIGS. READ FROM LOWER OR RIGHT HAND SIDE OF SHEET- 
MAKE ALL DIMENSIONS IN INCHES UP TO AND INCLUDING 36 INCHES. 
ANY DIMENSIONS NEED OCCUR BUT ONCE ON SAME DRAWING. 
DIMENSIONS OF PARTS OF A MACHINE REQUIRING GREAT ACCURACY 
SHOULD BE INDICATED ON DRAWING WITH PLUS AND MINUS 
ERROR THUS: DIAMETER OF SHAFT 3.625" ±%o%"" 
USE ENOUGH DIMENSIONS TO ENABLE THE PIECE TO BE MADE 
NO MORE-NO LESS! USE NOTES FREELY TO CLEAR UP DOUBTFUL 
POINTS. 
ALWAYS HAVE IN MIND THE WORKMEN WHO ARE TO USE THE 

DRAWING t THE PATTERN MAKER, BLACKSMITH AND MACHINIST. 
ALWAYS CONSIDER THE MACHINES AVAILABLE FOR THE WORK. 



-4 



64 MACHINE DRAWING 

PLATES 

Plates I to IV inclusive are to be made by the student as 
an examination on the work of Machine Drawing, Part I. These 
plates are to be the same size as those of the preceding Instruction 
Papers of the course, viz, 11 inches by 15 inches outside, with a 
margin of \ inch, making the clear space for the drawing 10 inches 

by 14 inches. 

PLATE I 

Sketches. From Plates II and III make rough, freehand 
sketches of the parts, paying no attention to scale or arrange- 
ment on the sheet. Simply make them of such size as to get them 
all on the standard sheet as specified. Use a medium pencil, and try 
to make the sketches quickly. Put on all the dimensions. Do not 
try to get smooth, straight lines, but dash off boldly with the pencil, 
aiming merely to get clearness and definiteness. Make the sketches 
over two or three times, noting any improvement in rapidity or 
effectiveness, and submit the best one. 

PLATE II 

Water Plunger. This represents the plunger for a water cylin- 
der of an ordinary pump. Make the drawing to a scale of 6 inches to 
the foot, and instead of copying the plate, use the sketch made on 
Plate I. This will not only give practice in working from a 
rough sketch, but will show whether all the information is on the 

sketch. 

PLATE III 

Valve Motion Details. This represents some of the details of 

the valve motion of an ordinary pump. Make the drawing to a 

scale of 12 inches to the foot, or full size, and as before, instead of 

copying the plate, use the sketches made on Plate I. Note that 

this plate requires the shade lines to be put on. This being a full size 

drawing, will stand very bold heavy lines, thus insuring a good blue 

print. This plate is to be made on tracing cloth, laid over the pencil 

work. 

PLATE IV 

Water Valve Details. This represents the complete valve 
mechanism for the water cylinder of an ordinary pump. Make the 
drawing to a scale of 12 inches to the foot, or full size. Although it 



MACHINE DRAWING 65 

is evident from the plate that this is a case where the dimensions can 
be placed on the assembly drawing without confusion, yet in order 
to give practice in detailing from an assembly drawing, the student 
is required to detail each part separately in the space to the right of 
the assembled valve as shown. The assembly view should first be 
made, copying the plate. Then, instead of placing the dimensions 
on the assembly view as shown, they should be placed on each indi- 
vidual detail as drawn. There are five parts to be shown, and the 
arrangement of these on the sheet, and the number of views necessary 
for each are left entirely to the student. This is a good opportunity 
to produce a nice, well-filled sheet, workmanlike in execution and 
arrangement, by exercising careful attention to the principles laid 
down in the foregoing pages. 

This plate should be made on tracing cloth laid over the pencil 
work. 



66 



MACHINE DRAWING 




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MACHINE DRAWING 

PART II 



MECHANISM DRAWING 

Study of Mechanisms. In Machine Drawing, Part I, working 
shop drawings have been analyzed in detail, systematic processes 
for making them have been outlined, and numerous illustrations 
given and thoroughly discussed. The student as yet, however, has 
not been shown how to originate the theoretical outlines of the 
surfaces controlling motion in machines; and it is the purpose of 
Part II to accomplish this. 

I The theoretical shape of the working surfaces of a machine can 
be studied and developed to best advantage without any considera- 
tion as to their strength or their ability to perform work or with- 
stand service. Such study is a study of the mechanism of a machine, 
and must always precede the study of design to provide the proper 
strength. 

A mechanism, therefore, is a combination of parts so formed 
and connected as to produce a desired motion, but not necessarily 
to perform any specific work. 

A machine is a working mechanism, or a combination of mechan- 
isms, suitably designed for the performance of specific work. 

Mechanism drawing is really the first step in machine design; 
and all the familiar parts of machines, such as springs, screws, cams, 
pulleys and belts, gears, etc., are dependent for their existing prac- 
tical form upon their theoretical layouts as mechanisms, involving 
exact mathematical principles. The student should pursue care- 
fully the study of motion as applied to the development of the com- 
mon machine parts, as this study is fundamental to the advanced 
work which follows it. 



70 



MACHINE DRAWING 



HELIX 

Development of Helix. Since most coil springs and all screw 
threads depend upon a curve known as a helix, it will be necessary 
to know what a helix is, and how it can be drawn, before taking up 
the construction of springs and screws. 

Suppose we take a cylindrical piece of wood, such as is shown 
in Fig. 51, and a rectangular piece of paper ABFE, with the side 
AB equal to the circumference of the cylinder, and the side AE 
equal to the length of the cylinder. If we lay off along AE any 





Fig. 51. Diagram of Simple Helix Construction 



convenient distance AD, and draw the line DC parallel to AB, we 
have the rectangle ABCD. Now draw the diagonal AC of this 
rectangle and wrap the paper around the cylinder, keeping the side 
AE on an element of the cylinder; the paper will just cover the 
cylinder, the edge BF meeting the edge AE. The point C coincides 
with the point D, and is on the same element of the cylinder as A; 
therefore the line AC has made one complete turn around the cylin- 
der, advancing the distance AD in this turn. The curve which the 
line AC now takes is called a helix, and the distance AD is called the 
pitch of the helix. 



MACHINE DRAWING 



71 



If on the piece of paper we also choose a point H, half way 
between A and D, and draw from this point a line HJ parallel to 
line AC, this line HJ will form another helix parallel to the helix 
formed by the line AC, when the paper is wrapped around the cyl- 
inder. The pitch of both helices is the same. 

The helix is often incorrectly called a spiral, but there is a 
marked difference between the two. The spiral is a curve which 
lies in one plane and winds around a point, constantly receding 
from the point, according to some law. The mainspring and hair- 
spring of a watch are in the form of spirals. 

Construction of Curve. To draw the projections of a helix we 
must know the diameter of the cylinder upon which the helix is 
formed, and the pitch of the helix. Fig. 52 shows the construction. 




Fig. 52. Diagram Showing Construction of Right-Hand Helix Curve 



Draw two projections of the cylinder ABDC; along any element, 
preferably one of the contour elements AB or CD, lay off the pitch 
AE. Divide the circumference of the circle, which is the end view 
of the cylinder, into any number of equal parts, and number the 
points of division 1, 2, 3, etc. Divide the pitch AE into the same 
number of equal parts, and number these points of division in the 
same way that the points on the circle are numbered, calling A point 
1. From point 2 on the circle, draw a line parallel to AB; and from 
point 2 on AB, draw a perpendicular to AB. The point L, where 
the parallel line meets the perpendicular line, is one point on the 
projection of the helix. The points M, N, etc., are found in the 
same manner. A smooth curve starting from A, going through all 
the points and ending at E, will be the projection of one turn of 
the helix. The half from A to R is on the front, and is, therefore, 



72 



MACHINE DRAWING 



a full line, while the half from R to E is on the back and is a dotted 
line. It should be observed that the point R is on the perpendicular 
from 7, which is just half-way between A and E; that is, the distance 



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Fig. 53. 



CI 23456789 JO II 12 1 
Diagram of Left-Hand Helix Curve 



CR is just one-half the pitch. The curve from E to B is the pro- 
jection of the next turn of the helix and is exactly like the first one. 

The helix shown in Fig. 52 is called a right-hand helix. If 
the curve starts at C and is drawn as in Fig. 53, we have a left-hand 
helix. Notice that the visible part (from C to R) slants in the same 
direction as the invisible part of the right-hand helix, which is 
shown dotted in Fig. 52. 

Since the helix is a line drawn on the surface of a cylinder, 
the other projection of the helix must be the circumference of the 
circle, which is the end view of the cylinder. Fig. 54 shows a right- 
hand double helix, and Fig. 55 is a right-hand triple helix. 

The construction of these curves should be studied carefully 
in order that springs and screw threads may be better understood. 




Fig. 54. Diagram of Right-Hand Double Helix 

Helical Springs. Accurate Representation of Springs. If, 
instead of winding a line around a cylinder in the form of a helix, as 
shown in the preceding figures, we wind a piece of spring wire, we 
shall get a helical spring. 



MACHINE DRAWING 



73 



Fig. 56 is the drawing of a helical spring of round wire, the side 
view only being drawn, as this is all that is necessary to give all the 
dimensions. To draw the spring we must know the pitch, the 




Fig. 55. Diagram of Right-Hand Triple Helix 

diameter of the wire, and either one of the dimensions A, B, or C 
If A is given, we subtract from A the diameter of the wire to find 
B; and if C is given, we add to C the diameter of the wire to get B; 
then, knowing B and the pitch, we can draw the helix (which is shown 
in dotted lines) exactly as the helix was drawn in Fig. 52. This is 
the helix formed by a line in the center of the wire. Now draw a 
series of circles with centers on this helix and of a diameter equal 
to the diameter of the wire. Smooth curves drawn tangent to these 
circles, as shown in the figure, will give the projection of the spring. 
Fig. 57 shows a helical spring of square wire. The drawing of 
this is simply the drawing of four helices, starting from each of 
the corners of the square ACML; this square being the cross section 
of the wire of which the spring is made. All four of the helices 




Fig. 56. Accurate Diagram for Helical Spring of Round Wire 

have the same pitch, equal to AB for, since the square BDP N is 
the same as ACML, the distance CD is the same as AB; and since 
the points L, M, N, and P are vertically under A, C, B, and D, 



74 



MACHINE DRAWING 



respectively, the distance LN is equal to AB, and MP is equal to 
CD. The helix AFB has a diameter equal to that of the circle IE, 
and is drawn by dividing the circle IE and the pitch AB, as in Fig. 




£• F G 

Fig. 57. Accurate Construction for Helical Spring of Square Wire 

52; and the helix CGD, having the same diameter as AFB, is drawn 
by dividing circle IE and pitch CD. The helix LHN has a diameter 
equal to that of the circle KR, which is IE minus twice the thickness 
of the wire, and is drawn by dividing up the circle KR and the pitch 
LN; and the helix MJP, having the same diameter as LHN, is 
drawn by dividing circle KR and pitch MP. Since the two circles 
are drawn about the same center, the divisions on circle KR can be 

found by drawing radial lines from the 
points of division on circle IE. The ver- 
tical lines drawn from the divisions of the 
pitch AB can be used for the divisions of 
L N; and those drawn from divisions of CD 
can be used for MP. 

After the four parallel helices are drawn, 
it is necessary to study the drawing care- 
fully, to decide what lines will be visible 
(full lines) and what invisible (dotted lines). 
Dotted lines should be used from H to J f 
N to P, etc., and full lines from F to G, B 
to D, etc. The line S T is the end of the 
spring, and consequently any part of a helix 
which goes outside of that line should not 
be left on the finished drawing. It is better, however, to draw in 
the whole of the square ACML, and to draw the helices starting 
from A to L, in order to draw those parts of the same helices 




Fig. 58. Conventional Draw- 
ing for Spring of Round Wire 



MACHINE DRAWING 



75 



which lie to the right of ST. The parts to the left of S fare 
shown in the figure by light, dotted lines to indicate that they 
are construction lines, and not a part of the projection of the 
spring itself. 

Conventional Representations of Springs. To draw springs by 
the method just explained involves considerable work and would 
consume a great deal of time if many were to be drawn; therefore, 
in working drawings, the draftsman commonly uses a conventional 
method. This conventional drawing is similar to the true projec- 






Fig. 59. Conventional Drawing 
for Square Wire Spring 



Fig. 60. Half-Sections of Round and 
Square Wire Springs 



tion, except that straight lines are used in place of curved lines. 
Fig. 58 shows the conventional drawing of a spring of round wire; 
and Fig. 59, of a spring of square wire. Springs are often shown in 
half-section, as in Fig. 60, this method involving less work than the 
method of Figs. 58 and 59. 



SCREW THREADS 

Screw and Nut. If we cut a groove around a cylinder in the 
form of a helix, we shall have what is called a screw thread, the thread 
being formed by the material which is left between the successive 
turns of the helical groove. A cylinder having such a helical groove 
cut around it is called a screw; and a piece having a cylindrical hole 



76 



MACHINE DRAWING 



in it, with a helical groove cut around the hole, is called a nut. The 
most common uses of the screw are to fasten pieces together, to hold 





Fig. 61. Simple Drawing for Left and Right-Handed V Screw Threads 

them at a given distance apart, and to cause one piece to move with 
relation to another piece. 

V Thread. The form of screw thread with which we are most 
familiar is what is known as the Y thread, shown in its simplest form 
in Fig. 61. Fig. 62 shows the method of drawing the true projections 
of this thread. The dimensions which must be known in order to 




OB D 

Fig. 62. Accurate Projections of the Right-Hand V Screw Thread 



make the drawing are the outside diameter AO, the pitch AC, and 
the depth of the thread AK. First draw the two projections of a 
cylinder of a diameter equal to the outside diameter of the screw. 
Half of the end view is sufficient. On the line AE of this cylinder 



MACHINE DRAWING 



77 



lay off AC equal to the pitch; starting at A, draw the helix A BCD, 
as described for Fig. 52. Inside of the cylinder AO, draw a smaller 



Al 



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Fig. 63. Accurate- Construction for Double V Thread 



cylinder KL, the diameter of which is equal to the diameter AO 
minus twice the depth of the thread. Now, on this smaller cylinder, 
starting at point H, perpendicularly under a point on the line AC 
which is half way from A to C, draw the helix L HJ with the same 
pitch as was used for the helix ABC. Draw the lines PR, X Y, ST, 





Fig. 64. Simple Drawing of Left- and Right-Handed Square Screw Threads 

etc., tangent to the two helices and the projection of the thread is 
completed. It is necessary to draw the invisible parts of the two 
helices in order to draw the lines ST, XY, etc. ; but they need not 
be left on the finished drawing. In Fig. 62 they are shown dotted 
for one turn of the screw, in order to indicate the construction. 



78 



MACHINE DRAWING 



Fig. 63 shows the method of drawing a double V thread. The 
process is exactly the same as for drawing a single thread. Start 
at point A, and draw the single thread ABCD exactly as in Fig. 62; 
then start at point 9, half way between A and C, and draw another 
single thread of the same pitch as the first one. Some thought may 
be necessary to decide when the lines of one thread become hidden 
behind the other thread. 

Square Thread. Another very common form of screw thread 
is that shown in Fig. 64, and known as the square thread. The 
method of drawing this thread is similar to that for the V thread, 
with the exception of a few minor points. The construction is shown 



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Fig. 65. Accurate Projections for Right-Handed Square Screw Threads 



in Fig. 65. The dimensions which must be known are the outside 
diameter AO, the pitch AC, the depth AH, and either the width 
of the thread AR, or the width of the groove RC. In the figure, 
the width of the thread AR is taken equal to one-half of the pitch; 
that is, AR and RC are equal. Beginning at A, draw the helix 
ABC; and beginning at R, draw the helix RMN, RN of course 
being equal to AC. Since the part between A and R is metal, 
forming the thread, there will be a line from A to R and from B to 
M, etc. Now, starting at point H, vertically under A, and at a 
distance from A equal to the depth of the thread, draw the helix 
HJV; and from S, vertically under R, draw helix S TW. Draw the 
lines S V, TK, etc. Here, as in the case of the V thread, the invisible 
lines must be drawn when making the drawing, but need not be 
inked. 



MACHINE DRAWING 



79 



Fig. 66 shows the construction of a double square thread. An 
explanation is not necessary, since the difference between this and 
the single square thread is practically the same as between the single 
and double V thread. 



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Fig. 66. Accurate Construction for Double Square Thread 



Typical Forms of V and Square Threads. The V and square 
threads are the two fundamental forms of thread in use, and all 
other forms are modifications of one or the other of these two. Figs. 
67 to 70 show some of the more common modifications. 

Figs. 67 and 68 show the two forms of the V thread which are 
commonly used in practice. 

U. S. Standard Thread. In Fig. 67 we have what is known as 



Fig. 67. U. S. 

Standard 

Thread 



Fig. 68. Whitworth 
Standard Thread 





Fig. 69. Lag Screw 
V Thread 



Fig. 70. Variation of 
Square Thread 



the Sellers or United States standard thread, an enlarged drawing 
of which is shown in Fig. 71. Referring to this figure, we see that 



80 



MACHINE DRAWING 



D~fM> or PITCH 

A = g OF D 




Fig. 71. Enlarged U. 6. 
Standard Thread 



the angle between the two sides of the thread is 60°, so that if the 
thread came to a point at the top and bottom, as indicated by the 
dotted lines, the depth of the thread D would be about T Vo of the 

pitch P. The sharp corners, however, are a 
disadvantage, since on the outside they are 
likely to be bruised and to give trouble in 
putting on the nut, and at the bottom of the 
groove they tend to weaken the bolt or screw. 
In order to avoid these sharp corners, the 
threads are flattened in the United States 
standard thread, as shown in Fig. 71, the 
amount of this flattening being such that the 
distance C is J of the pitch, or — what 
amounts to the same thing — the distance A 
is J of D. This gives a thread whose depth E is iVV of the pitch. 
Whitworth Standard Thread. Fig. 68 illustrates what is known 
as the Whitworth standard thread, shown enlarged in Fig. 72. Here 
the angle between the sides of the thread is 55°, so that if the threads 
came to sharp corners, as shown by the dotted lines, the depth D 
would be to 6 o of the pitch. The top and bottom of the thread, 
instead of being flattened, are rounded off so that the distance A is 
£ of D, or the depth E is T 6 /o of the pitch. 

Lag Screw V Thread. Fig. 69 shows the 
V thread as used on lag screws and other 
wood screws. Here the groove is much larger 
than the thread, because the wood into which 
it is to screw is weaker than the iron of which 
the screw is made. 

Variation of Square Thread. Fig. 70 
shows a slightly modified form of square 
thread, the only difference between this and 
the square thread previously described being 
that the sides of the groove taper slightly. 

Conventional Representations of Screw 
Threads. The student should 
the drawing of the threads, as previously ex- 
plained; and every draftsman should be able to draw the true pro- 
jection of a thread if he should have occasion to do so. It is evident 



A = / OF D 




Understand Fi S- 72 - Enlarged Whitworth 
Standard Thread 



MACHINE DRAWING. 



81 



however, that the process is complicated, and on a screw of small 
diameter and pitch it would be difficult to follow out the construc- 
tion. To avoid this labor the construction shown in Figs. 73, 74, 
and 75 may be adopted, straight lines being substituted for the 
projections of the helix. Fig. 73 shows the conventional representa- 
tion of the plain, single, right-hand V thread, the true projection of 
which was shown in Fig. 62. To make the conventional drawing 
(Fig. 73), draw the parallel lines AB and CD at a distance apart 
equal to the outside diameter of the screw, and draw the line AC 
perpendicular to these two lines. Along A, lay off the distances AE, 
EF, etc., each equal to the pitch. Along CD, lay off CH equal to \ 
the pitch; and from H, lay off 
HI, IJ, etc., equal to the pitch. 
Draw lines from A to H, E to 
I, etc. Now, if the depth of the s 
thread ^4>S is known, draw the 
lines ST and UV; and begin- 
ning at L, perpendicularly under 
a point halfway between A and 
E, lay off LM, MN, etc., equal 
to the pitch. In like manner 
find the points 0, P, R, etc., and 
draw the lines LO, MP, etc.; 
also AL, LE, HV, HO, etc. 
The dotted lines should be left 
out in the finished drawing, but are put in the figure to show the 
construction. 

If, instead of knowing the depth AS, we know the angle between 
AL and LE, the depth can be found by drawing from A and E the 
two lines AL and EL in such a way that they make the required 
angle with each other. To do this, the lines AL and EL should 
each make an angle with the line AB equal to 90° minus \ the angle 
between AL and LE. 

Fig. 74 shows the corresponding construction for the United 
States standard thread. Draw the lines AB, CD, and AC as in 
Fig. 73, and find the points E, F, G, H, I, J, K, etc., in the same way 
as in that case. Now draw the lines S T and UV so that AS and 
CU shall equal tVo of the pitch AE. On the line AB, lay off from 




H 
Fig. 73 



Conventional Drawing for Right- 
Hand V Thread 



82 



MACHINE DRAWING 




Fig. 74. 



Conventional Drawing for U. S. 
Standard Thread 



A a distance Al equal to T V of the pitch; and on each side of E, F, 
G, H, etc., lay off E2, E3, etc., each equal to iV of the" pitch. From 

the points thus found, draw lines 
1 — 4 > ® — 5> etc., making an 
angle of 60° with AB. The rest 
of the drawing is completed as 
shown by drawing in full lines 
those parts of the lines AB, CD, 
ST, and UV intercepted be- 
tween 1 — 4 and 2 — 5, etc. 

Fig. 75 shows the conven- 
tional representation of a square 
thread, and is drawn in exactly 
the same way as the true pro- 
jection shown in Fig. 65, except 
that straight lines are used instead of curves, and certain other 
minor lines omitted. 

Square threads are seldom conventionalized more than as 
shown in Fig. 75, and V threads of coarse pitch and large diameter 
are usually drawn as in Fig. 73, whether sharp or U. S. standard. 
But for ordinary screws of small diameter and fine pitch, as are most 

frequently used, such a method involves 
too much labor, and the use of alternate 
long and short dashes across the body of 
the screw, as shown in Machine Drawing, 
Part I, Fig. 14, is universally employed. 

CAMS 

Mechanical Action. A cam is an ap- 
plied form of the ordinary wedge. The 
simple wedge is used to split apart the piece 
into which it enters, or to pry up heavy weights. It does not 
automatically repeat its work. The work of the wedge is fin- 
ished when it is once driven home; and its function is not to 
produce motion, but to give mechanical advantage to the blows 
which drive it. 

If we take a simple wedge and fasten it to some piece — say, a 
disk centered on a shaft, which is capable of continuous or periodic 




Fig. 75. Conventional Draw 
ing for Square Thread 



MACHINE DRAWING 



83 



FOLLOWER 



WEDGE 



rotation, and allow the face of the wedge to rub against another 
guided piece, called the follower, we have a cam. In Fig. 76 is 
shown a double wedge in which either sloping side produces against 
the follower the action just referred to. When we rotate the 
cam, it "wedges" the follower along a fixed path. When the fol- 
lower reaches the top of the wedge, it may drop back to its original 
position, drawn by gravity or by the force of a spring, or it may be 
eased back by another wedge in the reverse position of the other, 
as shown in Fig. 76. This cycle will be repeated as long as we choose 
to rotate the cam. The cam, therefore, is essentially a repeating 
wedge, and its function is primarily one of motion rather than of 
great force. The wedge principle, however, enables very powerful 
cams to be made in cases where but little 
motion is desired. The motion of the 
cam is usually a rotation, but it may be an 
oscillation, or a straight-line reciprocating 
motion. 

Factors in Design and Layout. In 
designing a cam, it is not only essential 
that the proper layout be made to pro- 
duce, theoretically, the required motion of 
the follower, but that the wedge action be 
such that the cam will drive easily. Re- 
ferring again to the wedge as a machine, 
a thin wedge, for example, may be forced 
under a heavy weight with a sharp blow, 
whereas a thick broad wedge cannot be 
made to lift the weight. For precisely the same reasons, cams 
designed with thin wedges will drive their followers with ease, 
while cams may be designed so steep in their wedge action that they 
drive with difficulty, and may even lock the follower in its path, on 
account of excessive side pressure. This is a very important ele- 
ment in a design, and the analysis will be brought out more clearly 
in the discussions of. the line of pressure. 

The actual laying out of a cam is simple in principle, although 
somewhat tedious, especially in complicated cams. Several posi- 
tions of the follower in its path are chosen, the .follower drawn in 
those positions, and then the face of the cam is drawn tangent 




Fig. 76. Simple Diagram of a Cam 



84 



MACHINE DRAWING 




thereto. In order to do this, the several positions of the follower 
in its path may be laid down on the drawing paper as shown in Fig. 
77. This fixes the limit through which the cam 
must move the follower. Now develop the cam 
itself on a separate piece of transparent paper or 
tracing cloth, Fig. 78, and place this over the 
follower layout with the centers of the two draw- 
ings coinciding, and a pin through this center of 
rotation of the cam. As the cam is rotated 
about this axis so as to correspond to the various 
positions of the follower shown on the drawing 
underneath, the follower can be traced in on the 
Follower upper drawing in each position. 

When the movement of the cam is complete, 
we have on the cloth a series of drawings of 
the follower; and, if we draw a tangent line 
to these, the line of the cam will be produced. 
This method, however, from the drawing-board 
centerof cam standpoint, is clumsy and inaccurate, because of 
Fig. 77. Layout for Posi- the wearing of the pinhole and the error of trans- 

tions of Cam Follower „ , . „ . „ „ . . 

ierrmg the shape or the lollower to the tracing 
cloth. It is readily seen by reference to Figs. 77 and 78, that the 
same result will be attained in a much easier and more accurate 
manner if we artificially rotate the follower about the cam on the 
drawing-board by means of a pair of compasses, laying off equal 
angles to complete one revo- 
lution of the cam and show- 
ing the follower in position at 
each step. This is shown in 
Fig. 81, and is the method usu- 
ally followed in cam design. 
This does not mean that the 
tracing-cloth method should be 
discarded, for it is useful in 
studying complicated cam move- 
ments; and also in testing the 
cam development when it is completed, to make sure that no error 
has been made. 




-#^ 



Fig. 78. Layout for Cam 



MACHINE DRAWING 85 

PRACTICAL EXAMPLES IN LAYING OUT CAMS 

Statement of Problems. From the principles just stated, the 
uniform course of procedure in laying out a cam is as follows: 

1. Draw the follower in several positions in its path. 

2. Draw cam radii corresponding to these positions. 

3. Rotate the follower about the cam. 

4. Draw tangent line. 

5. Test the cam. 

6. Draw the line of pressure for each position. 

Plate Cams with Uniform Motion 

In Figs. V"9 to 86 inclusive, it is required to move the follower F 
with uniform motion from position to 6, while the cam rotates 
through 450°; it is then to remain at rest during a cam movement 
cf 30° ; then to return to its original position, moving uniformly from 
position 6 to 0, while the cam turns through the remainder of the 
circle, or 180°. This is briefly expressed as follows: Uniform rise^ 
150°; rest, 30°; uniform fall, 180°. 

Example 1. Pointed Follower with Path Intersecting Cam 
Center. 1. Follower Positions. The length of travel 06, Fig. 79, 
is supposed to be known, being fixed by some requirement of the 
machine to which the cam is to be applied. This distance, for a 
uniform motion, should be divided into any convenient number of 
equal parts; the more divisions, the more accurately can the cam be 
drawn. In this case six spaces are chosen. 

2. Cam Radii. The diameter of base circle D is arbitrary; 
and its center having been chosen, draw the original radius CO; then 
the radii CX and CB, limiting the arcs of rise, rest, and fall, res- 
pectively, should be drawn. As the follower must rise J of its travel 
while the cam rotates \ of its arc, there must be as many equal 
divisions of the cam arc as there are of the follower travel. Hence 
the arc of rise OX is divided into six equal parts and the radii are 
drawn. Similarly, the arc of fall OB is divided into six equal parts 
and the radii produced. 

3. Follower Rotation. The rotation of the follower about the 
cam is accomplished by setting the point of the compasses at C, and, 
with radius Cl, striking an arc intercepting the radius corresponding 
to position of the follower at R v Similarly, points R 2 , R 3 , R v i? 5 , 



86 



MACHINE DRAWING 



and i? 6 are found. As the follower rests from X to B, the arc of 
intersection for jR 6 is continued to F 6 . For the period of fall, arcs 
are swung from the same points of follower travel as before, making 
the intersections F h , F v F 3 , F 2 , F v 

4. Tangent Line. A smooth curve is now drawn through the 
points of intersection, thus forming the outline of the cam. For 
other forms of follower than a sharp point, this line would be strictly 




Fig. 79. Diagram for Cam with Pointed Follower Whose Path Intersects Cam Center 

a tangent line to the face of the follower. A pointed follower, as 
shown in the figure, is not a very practical form, as the point is 
subjected to severe wear. It is chosen for the present illustration, 
to afford the simplest possible cam development. 

5. Testing. The cam may be tested by laying over it a piece 
of tracing cloth, and tracing roughly the outline of the cam, also 
marking the radii and the center of rotation. A pin is now placed 
at the center of rotation of the cam, and the tracing cloth swung 



MACHINE DRAWING 87 

until the several radii CR V CR 2 , CR 3 , etc., fall into the line of travel 
C T. If the cam is correctly developed, it will just touch the several 
positions of the follower in its path when the proper radius is coin- 
cident with the line of travel C T. It is very easy to make a mistake 
in laying out cams, especially the more complicated ones; and this 
rough method of proving the work should always be applied. 

6. Pressure Line. The face of the follower in this case is a 
point, and the pressure line, being the common normal between the 
cam and follower at point of contact, is always theoretically normal 
to the cam at that point. 

During motion, however, the force of friction between the cam 
and follower would modify somewhat the direction of the pressure 
line, turning it so as to produce a side thrust against the follower, 
causing consequent chattering and possible binding in its guides. 
This can be minimized by ample lubrication and hardened faces; 
but for cams which have any considerable load to work against, a 
follower carrying a roll against the cam is a necessity. 

The line work in cam design should be fine and accurate. A 
hard pencil, kept well sharpened, is necessary, and special care must 
be taken to get definite intersections. In order to keep the center of 
the cam in as good condition as possible, it is well not to continue 
the radii to the center, but to stop when a short distance from 
the center, as shown. When penciling and inking in, use a fine, 
continuous line, not dotted; the continuous line is more quickly 
made and is apt to be more accurate than the dotted line. More- 
over, the cam is strictly layout work, not finished in detail, and the 
subsequent detail drawing of the cam should not be confused with 
the layout of the cam outline. 

Example 2. Pointed Follower with Path Not Intersecting Cam 
Center. 1. Follower Positions. The follower positions, Fig. 80, are 
chosen and drawn precisely as in Fig. 79; in this case, however, the 
path of the follower does not intersect the center of the cam, but, 
if produced, would pass at some distance to one side of it. This 
changes materially the development of the cam, as will subsequently 
be noted. 

2. Cam Radii. The diameter of base circle and center of cam 
being chosen as before, draw the original radius CO. This original 
radius is the one to which all subsequent radii are related. Treating 



88 



MACHINE DRAWING 



this radius the same as the original radius CO in Fig. 79, the radius 
CX is drawn, making the arc of rise 150° as before. The radius CB 
is then drawn, giving the 30° arc of rest, and leaving the arc of fall 
between CB and CO 180° as before. Since the cam is to have 
uniform motion, the subdivisions of the arcs are equal, and are made 
in exactly the same manner as in Fig. 79. 

3. Follower Rotation. The follower is now rotated about the 
cam by the compasses, in similar manner to that in Fig. 79, pro- 




Fig. 80. Diagram of Cam with Pointed Follower Off Center 



ducing the intersections R v R 2 , R 3 , R v etc. Now, however, the 
introduction of a new step should be noted. The original radius CO, 
not being coincident with the path of the follower OT, the inter- 
sections R iy R 2 , R 3 , etc., do not represent the actual positions of the 
point of the follower when rotated. During the arc of rise, the 
follower is gaining on the radius, and the increasing distances R t L lf 
R 2 L 2 , R 3 L 3 , etc., must be set off ahead of the radii, equal to the 
distances HI, K2, J3, etc. In similar fashion, during the arc of 



MACHINE DRAWING 89 

fall, the decreasing distances FqN 6 ,F 5 N 5 , F 4 N v F 3 N 3 , must be set 
off ahead of the radii, equal to Q6, P5, M4, JS, etc. 

' 4. Tangent Line. A smooth curve is now drawn, not through 
the original points of intersection with the cam radii, as in Fig. 79, 
but through the points set off as above from these intersections. In 
other words, the cam curve is drawn through points L v L 2 , L 3 , L v 
etc., and iV 6 , iV 5 , N v N 3 , etc. 

5. Testing. A piece of tracing cloth should be laid over the cam, 
the outline traced upon it, the radii marked, and then the tracing cloth 
rotated about the pin point, as in Fig. 79, to see if the cam in its suc- 
cessive positions just touches the follower in each of its positions. 

6. Pressure Line. The pressure line at each position of the 
follower is, as in Fig. 79, normal at the point of contact. 

Example 3. Roll Follower with Path Intersecting Cam Center. 

1. Follower Positions. In Fig. 81, the case is identical with that 
of Fig. 79, except that the shape of the follower has been changed to 
the more practical form of a roll, which can turn about a pin, thus 
relieving the crowding, grinding action characteristic of the pointed 
follower hitherto discussed. The path of follower roll F is divided 
as before into six equal parts. 

2. Cam Radii. The original radius CO, the radius CX, 
limiting the arc of rise, the radius CB, limiting the arcs of rest and 
fall, are all drawn precisely as before, and the subdivisions of the arcs 
are in nowise changed from the preceding cases. 

3. Follower Rotation. The follower is now rotated about the 
cam, giving the intersections R v R 2 , R 3 , R 4 , R 5 , and R & for the period 
of rise; the corresponding intersections for the period of fall are 
F 6 , F 5 , F v F 3 ,F 2 , and F v With each of these intersections as a center, 
and a radius equal to the radius of the follower roll, an arc is struck, 
which represents the follower in its rotated position. 

4. Tangent Line. A common tangent line is now drawn to the 
several positions of the rotated follower, giving the outline of the 
cam as a smooth curve. In order to give the follower its full period 
of rest from R Q to F G , the portion of the cam lying between the radii 
CX and CB must be a true arc of a circle struck from center C. 
Special attention must be paid to this point, because, if the true arc 
is not maintained between these radii, the full period of rest will not 
be secured. 



90 



MACHINE DRAWING 



5. Testing. The testing of the cam is accomplished in the same 
way as previously described, by the tracing-cloth method. The 
several positions of the follower in its path should be drawn; and as 
the cam is rotated into its several positions, if the work has been 
accurately done, the cam will be perfectly tangent to each position 
of the follower. 

6. Pressure Line. By a well-known principle of mechanics, 
when two bodies are in contact, the line of pressure between them is 




Fig. 81. Diagram of Cam with Roll Follower on Center Line 

always perpendicular to the surfaces at their point of contact; in 
other words, the line of pressure is the common normal at the point 
of contact. The follower being a true circle, the perpendicular 
at any point of its surface must pass through the center of the roll; 
therefore, if we draw a line from the center of each position of the 
roll to the point of contact between it and the cam, this line will 



MACHINE DRAWING 91 

be the line of pressure between the cam and the roll. This has been 
done in Fig. 81, ard the arrows indicate the direction of the pressure 
of the cam against the roll. In order to group these lines of pres- 
sure so that the action may be clear as the follower moves over its 
path, the lines of pressure as drawn are rotated back to the corres- 
ponding points in the path of the follower. By this it is readily seen 
that during the period of rise the lines of pressure are all slightly 
inclined towards the left of the line of travel, while during the period 
of fall the lines of pressure are all slightly inclined towards the right. 
The cam as shown in Fig. 81 is a very good cam, so far as the lines of 
pressure are concerned. The ideal condition would be to have the 
lines of pressure all coincident with the line of travel. This is impos- 
sible, because the only shapes which would give a common normal 
along the line of travel would be two circles, revolving about their 
centers, and such a cam could give no travel to the follower. The 
fact that the lines of pressure are at such a slight angle to the 
line of travel indicates that there is very little side pressure on the 
follower and that, therefore, the cam will be an easy working cam. 

Example 4. Roll Follower with Path Not Intersecting Cam 
Center. 1. Follower Positions. The follower positions in Fig. 82 
are chosen precisely as in Fig. 81, and the subdivisions of the path of 
the follower similarly made. This case corresponds with that of 
Fig. 80, the line of travel not intersecting the center of the cam. 
The shape of the follower, however, is a roll similar to that just 
discussed in Fig. 81. 

2. Cam Radii. The original radius CO is drawn as before. 
Then the radius CX, limiting the arc of rise, the radius CB, limiting 
the arcs of rest and fall, and the subdivisions of the arcs of rise and 
fall, are made exactly as in Fig. 81. 

3. Follower Rotation. The treatment of follower rotation is 
the same as that in Fig. 80. The intersections R v R 2 , R 3 , etc., being 
found, the distances R t L v R 2 L 2 , R 3 L 3 , which the follower gets ahead 
of the radii, are set off exactly as in Fig. 80. In this case, however, 
the points L v L 2 , and L 3 are the centers of the rotated follower roll; 
and from these centers are struck the arcs representing the follower 
roll in its several rotated positions. 

4. Tangent Line. A smooth tangent line is now drawn to the 
several positions of the rotated follower, thus giving the outline of 



92 



MACHINE DRAWING 



the cam. In this case the outline of the cam giving the period of rest 
lies between the radii CN 6 and CL 6 . In order that the full period 
of rest may be accomplished, it is necessary that the portion of the 
cam between these two radii be a true arc, struck from center C. 
Special attention should be given this point. 

5. Testing. The cam should be tested by the tracing-cloth 
method, as before. 

6. Pressure Line. The pressure lines are drawn as in Fig. 81 




Fig. 82. Diagram of Cam with Roll Follower off Center 



by joining the center of the follower roll in its rotated positions to 
the point of contact between the cam and the roll. 

Arrows, as before, indicate the direction of the pressure. These 
pressure lines may be rotated until they are collected along the line 
of travel, indicating the change in direction of the pressure between 
the cam and the roll as the roll passes over its path. A convenient 



MACHINE DRAWING 



93 



method of laying off these pressure lines is to join the center of the 
cam C with the center of each roll ; measure the angle which the line 
of pressure makes with this radius; and then transfer the angle to the 
proper point on the line of travel. This method is clearly indicated 
in the figure. 

As before, it will be seen that the line of pressure lies quite close 
to the line of travel, and therefore the cam will be an easy working 
cam. 

Example 5. Roll Follower Mounted on Oscillating Arm. 
1. Follower Positions. In Fig. 83 the follower is a roll, as before; but 




Fig. 83. Diagram of Cam with Roll Follower on Oscillating Arm 

instead of traveling in a straight line, it is made to travel along the 
arc of a circle, being carried on the end of an arm OC , C being a 
fixed point about which the arm oscillates. The length of travel 06 
is the same as before, and is likewise divided into six equal parts. 
This method of carrying the follower roll is, perhaps, the most com- 
mon of all, and is a very effective plan for giving the follower roll 
easy movement along its path. 



94 MACHINE DRAWING 

2. Cam Radii. The original radius CO is drawn in this case, 
as in all the others, through the original center of the follower 
roll. The radii CX and CB, limiting the arcs of rise, rest, and fall, 
are likewise drawn in the given relation to the original radius CO, 
and the arcs subdivided precisely as before. 

3. Follower Rotation. For the purpose of follower rotation, 
arcs are now struck through the points 1,2,3, 4, 5, and 6, these arcs 
being prolonged until they meet the original radius in the points 
H, K, J, M, P, and Q. Then the rotation of the points H, J, K, etc., 
produces the intersections R lt R 2 , R 3 , etc.; but it should be noted 
in this case that the follower roll, instead of getting ahead of the 
radius, as in Figs. 80 and 82, is lagging behind it at each position. 
The distances R 1 L V R 2 L 2 , R 3 L 3 , R±L V R 5 L 5 , while being laid 
off equal to Hi, K2, J3, M4, P5, Q6, etc., as in Figs. 80 and 82, 
are laid off behind the radius in each position on the arcs of rise and 
fall. These distances are constantly increasing up to point 6, where 
the roll remains stationary during the period of rest, and then con- 
stantly decrease to zero, until the roll reaches the original position 
at point 0. From the points just found, arcs are struck as before, 
the radius being equal to the radius of the follower roll. 

4. Tangent Line. The tangent line is drawn as a smooth 
curve to these arcs, and the arc of rest is struck as before, thus 
developing the outline of the cam. 

5. Testing. The cams should be tested by the tracing-cloth 
method as before. 

6. Pressure Line. The pressure lines are drawn precisely as 
in Figs. 81 and 82; but it is a little more difficult to rotate these 
pressure lines back to the points in the path of the follower, and 
the tracing-cloth method is suggested as best for this purpose. This 
is done by taking a scrap piece of tracing cloth, fixing a pin through 
it to the center of the cam, tracing upon it, from the paper below, the 
pressure lines and the centers of the follower. These centers being 
rotated back until coincident with the corresponding points of the 
travel, a second point in each pressure line is pricked through on the 
paper below. Upon the removal of the tracing cloth, each pressure 
line can then be quickly drawn through these pricked points and the 
corresponding centers of the follower, thus enabling the action of the 
cam to be properly judged. 



MACHINE DRAWING 



95 



Example 6. Pointed Follower Mounted on Oscillating Arm. 

In Fig. 84 the follower roll has been abandoned, and the original 
pointed follower substituted. The motion of the follower point, 
however, instead of being in a straight line, is in the arc of a circle 
precisely as in Fig. 83, except that the follower, being a point instead 
"of a roll, the points L t , L 2 , L 3 , etc., have the outline of the cam 
drawn directly through them. This case is introduced merely for the 




Fig. 84. Diagram of Cam with Pointed Follower on Oscillating Arm 

purpose of making the set of cams complete, and it is so closely a 
counterpart of Fig. 83 that the detail study of it is considered un- 
necessary. 

Example 7. Flat Follower with Path Perpendicular to Working 
Face. 1. Follower Positions. In this example, Fig. 85, is introduced 
a follower with a flat surface, its path being perpendicular to its 
working face. The length of its path 06 is the same as before, and 
is divided into six equal divisions. 



96 



MACHINE DRAWING 



2. Cam Radii. The point of original contact being chosen, 
the original radius OC is drawn .perpendicular to it; the radii CX 
and CB, limiting the arcs of rise, rest, and fall, are then drawn in 
their proper relation to CO, and the arcs of rise and fall subdivided 
as before. 

3. Follower Rotation. The intersections R v R 2 , R 3 , R v etc., 




Fig. 85. Diagram of Cam with Flat Follower Perpendicular to Working Face 



of the rotating arcs with the several positions of the radii, are found 
as before. The rotated positions of the follower in this case are 
obviously represented by drawing perpendiculars to the several radii 
through the points R v R 2 , R 3 , R v etc. 

4. Tangent Lines. The outline of the cam is produced by 



MACHINE DRAWING 97 

drawing a tangent line to the several lines representing the rotated 
positions of the follower, the arc of rest being struck as before. 

5. Testing. The cam should be tested by the tracing-cloth 
method. 

6. Pressure Line. Pressure lines are drawn at the points of 
contact between the cam and the follower, by erecting perpendiculars 
to the face of the follower at these points. As in the case of the 
pointed follower, there is considerable friction due to the sliding of 
the cam along the follower face. This friction produces a side thrust 
perpendicular to the path of the follower, and modifies the pressure 
lines slightly. If it were not for this friction, the pressure line 
obviously would always be perpendicular to the follower face, acting 
at a point on the follower face some distance to one side of the original 
point of contact 0. By taking the distances R t TJ V R 2 U 2 , R 3 U 3 , etc., 
to the several contact points, and rotating them back, the manner 
in which the point of contact between the cam and the follower moves 
along the face of the follower during its travel can be conveniently 
studied; it is seen that the point of contact during the arc of rise 
moves to the right of the original radius, and gradually swings back 
again until, at the point 6, it is on the line of the original radius. 
During the arc of rest, the point of contact remains at point 6; during 
the arc of fall, it moves to the left of the original radius, finally coming 
back again to the original point of contact 0. 

Example 8. Flat Follower Mounted on Oscillating Arm. 
1. Follower Positions. In this example, Fig. 86, a flat-faced follower 
is carried by an oscillating arm similar to the roll in Fig. 83. The 
length of travel 06 is divided into six equal parts, as in the previous 
cases, the positions of the follower being indicated by the radial 
lines C'l, C% C'8, etc. 

2. Cam Radii. The original radius CO is drawn through the 
assumed point -of contact, and perpendicular to the face of the 
follower in its original position. (The radii CX and CB are then 
drawn limiting the arcs of rise, rest, and fall, and the subdivisions of 
the arcs of rise and fall properly made. 

3. Follower Rotation. The intersections R v R 2 , R 3 , etc., of 
the rotating arcs are found as in the previous cases. The rotation 
of the follower is accomplished by drawing through the points R v 
R 2 , R 3 , etc., straight lines making the same angle with these radii as 



98 



MACHINE DRAWING 



the follower in its corresponding positions makes with the original 
radius CO. For example, the angle a t is equal to a; the angle b t is 
equal to b; and the angle c 2 is equal to c. 

4. Tangent Line. The tangent line is now drawn to the several 
positions of the rotated follower, and the arc of rest is struck, thus 
giving the outline of the cam. 

5. Testing. The cam should be tested by the tracing-cloth 
method. 

6. Pressure Line. The pressure lines are drawn the same 




Fig. 86. Diagram of Cam with Flat Follower on Oscillating Arm 

as in Fig. 85, and it is suggested that the rotation of them back to the 
positions of the follower in its path be accomplished by the tracing- 
cloth method, as in Fig. 83. 

Design of Complicated Cams. It should be especially noted, 
that in all the cases of cams thus far studied, the methods of pro- 
cedure are absolutely identical. In the more complicated cases of 
cams which follow, and others which may arise in the designing of 



MACHINE DRAWING 99 

special machines, the same principles apply, however much they may 
apparently be disguised by the conditions of the problem. A good 
method to follow in designing a complicated cam is first to study 
the cam by the tracing-cloth method, as described on page 84. After 
an approximate outline of the cam has been determined as being 
possible, and giving about the motion of the follower desired, then 
the more formal method of rotating the follower about the cam can 
be applied, to give the exact outline. It should be remembered that 
it is not possible to reproduce by cam movements all combinations 
of length of travel, angle of rest, rise, and fall, as fixed by the con- 
ditions of the problem. In such cases the cam is designed to 
give the nearest possible approach to the motion desired, or some 
of the working conditions are changed. 

In each of the cases considered, it has been assumed that the 
follower is always held against the surface of the cam, either by its 
own weight or by a spring. Another method of accomplishing this 
is to make a cam with two surfaces, the follower running between 
them in the groove thus formed. 

Plate Cams with Complex Motions 
Uniform Motion. All cams thus far considered are of the uni- 
form-motion variety, that is, having equal rise in equal time. This 
means that each fraction of the travel of the follower is made in the 
same time as each other similar fraction; and likewise, that each 
fraction of the rotation of the cam is made in the same time as that 
of any other fraction of its movement. In further explanation of the 
term "uniform motion", suppose a railway train to travel ten miles 
in twenty minutes, the speed of the train being the same during each 
minute; it would travel \ mile in each minute, and would have a 
uniform speed or velocity of \ mile per minute. Under such con- 
ditions the train would be moving at the full speed of \ mile per 
minute, both at the beginning and at the end of the ten miles. If, 
however, it had exactly ten miles to travel and exactly twenty 
minutes to do it in, and must be at rest at the beginning and at the 
end of the given time, it could not gain its full speed in an instant 
or lose it in an instant, but must start and stop gradually. There- 
fore, during the first part and the last part of the time, it would be 
moving at a speed slower than \ mile per minute, and must go faster 
than \ mile per minute during the middle part of the run, to make 



100 



MACHINE DRAWING 



up for the time lost in starting and stopping. Such motion would 
not be uniform. The more suddenly the train starts and stops, the 
more nearly uniform the main part of the travel may be, but the 
greater the shock when starting and stopping. 

Suppose we have a piece to be moved one foot in ten seconds; 
if the motion is to be uniform, the piece would have a velocity of T V 
foot per second. If the piece is light and the mechanism which does 
the moving is sufficiently powerful, the piece may be made to start 
and stop almost instantly without serious shock, and consequently 
may have practically uniform motion. 

Variable Motion. If the mechanism which moves the piece be 
so designed as to start and stop it gradually, the shock will be avoided. 
We may have a gradual increase of speed at the start, until full speed 
is attained; then a uniform full speed during the main part of the 
stroke; and finally a gradual decrease of speed to a full stop at the end 
of the stroke; or the speed may increase during the entire first half 
of the stroke, and decrease during the entire last half, the motion at 

no time being uniform. The first 
condition is used where the piece 
is doing work during the stroke, 
as, for instance, the cutting stroke 
of a tool; and the second condi- 
tion, wherever quick motion is 
desired without regard to its 
character, so long as it is without 
shock. 
Harmonic Motion. In Fig. 87, let the semicircle ABD repre- 
sent the path along which a piece moves with a uniform velocity. 
Now, if we have another piece moving along the diameter AD, 
starting from A at the same time as the first piece, and moving at 
such speed that a perpendicular let fall from any position of the first 
piece to the line AD will locate the second piece-^that is, when the 
first piece is at C, the second piece is at E; when the first piece is at 
B, the second is at 0; and so on— then the piece which travels along 
the line AD has harmonic motion. It moves slowly at first, increases 
to a maximum speed at the center, and decreases to rest at the end. 
This motion is quite common for shaper rams, slotters, and feed- 
mechanisms. Cams can readily be designed to give such a motion. 




Fig. 87. 



o E A 

Harmonic Motion Diagram 



MACHINE DRAWING 



101 



Uniformly Accelerated and Retarded Motion. A piece which 
has uniformly accelerated and uniformly retarded motion (see article 
on Mechanism) moves through one unit of space in the first unit of 
time, three the second, five the third, seven the fourth, nine the fifth, 
etc., to the middle of its stroke, then decreases at the same rate to 
the end of the stroke. For example, if a piece is to move with 
uniformly accelerated and retarded motion one foot in ten seconds, it 
will move T V foot the first second, -§-%- the second, j% the third, j\ the 
fourth, 5V the fifth, when it will have traveled T \ +/ +jo+-g\+-iv 
( = ||) j or \ the whole foot in one-half the 
whole time, the speed increasing all the time ; 
at the end of the fifth second, when half 
the distance has been traveled, it begins to 
slow down, and travels 5V the sixth second, j\ 
the seventh, T V the eighth, ¥ \ the ninth, and 
-o the tenth. The rate at which the velocity 
increases during the first half of the time is 
often made the same as that at which the 
velocity of a weight increases when dropped 
from a height; and the rate at which the 
velocity decreases during the last half of the 
time, the same as that at which the velocity 
of a weight decreases if thrown straight up 
into the air. This particular form of uniformly accelerated and uni- 
formly retarded motion is, therefore, known as gravity motion. It 
is commonly produced by cams, although not often used for motions 
greater than a few inches. 

If in Fig. 79 it had been required to raise and lower the follower 
with harmonic instead of uniform motion, the only difference in 
procedure would have been in dividing up the path 06. The divi- 
sions of 06, instead of being equal, would be found as shown in Fig. 
88. Suppose the line Ae to be the same length as 06; on this line as 
a diameter, draw a semicircle, and divide this semicircle into as many 
equal parts as the arc of rise is divided. In this case, suppose the arc 
of rise to be divided into 8 equal parts; then the semicircle is like- 
wise divided as shown in the figure. From the points B, C, D, etc., 
drop perpendiculars to the line Ae, cutting it at points 1, 2, 3, etc. 
For the first eighth of the arc of rise of the cam, let the follower rise 




Fig. 88. Semicircle Show- 
ing Harmonic Steps 



102 MACHINE DRAWING 

the distance A-l, for the second eighth the distance 1-2, for the 
third eighth the distance 2-3, and so on. Such motion of the follower 
is harmonic motion. 

If it is required that the follower shall rise and fall with uniformly 
accelerated and retarded motion, the method of dividing the line 
of travel Ae is shown in Fig. 89. As in the case of harmonic motion, 
suppose the arcs of rise and fall each to be divided into 8 equal parts. 
Now, the line Ae must be divided into 8 parts, but these parts must 
be such that, beginning with the point A, the distances A-l, 1-2, 2-3, 
and 3-4 shall be in the ratio of 1, 3, 5, and 7; and the distances 4-5, 
5-6, 6-7, and 7-e shall be in the ratio of 7, 5, 3, and 1 ; in other words 
A-l is ¥ V of the whole line Ae; 1-2 is s \ of Ae, 2-3 is T V of Ae, and 
so on. To divide up the given length Ae so that the divisions may 
bear the above relation to one another, draw the line Ar at any con- 

. venient angle, and, choosing 

/r 

any convenient distance as a 
unit, mark it off on this line 32 
times, beginning at A. From I, 
the last of these dividing points, draw 
a line to e; next find the point B, the 
first division from A; C the third from B, D 
the fifth from C, E the seventh from D, F the 
seventh from E, G the fifth from F, H the 
third from G; and through the points H, G, F, E, 
etc., draw lines parallel to Ie, cutting the line Ae at 
7, 6, 5, 4, etc. It is obvious that Ae is then divided 
in the same proportion as AI, and if the follower were 
of Dividing Line made to travel along the line Ae according to these 

of Travel & ■ 

divisions, it would have uniformly accelerated and 
retarded motion. 

Practical Example of Complex Motion Cam. For the purpose 
of illustrating these principles, suppose it is required to design a 
plate cam, Fig. 90, such that the follower rises from point A to e, 
with harmonic motion, while the cam rotates through 120°; it is then 
to remain at rest during the cam movement of 60°; it is then to fall 
to its original position with a uniformly accelerated and retarded 
motion, while the cam turns through 150°; it is then to remain at 
rest while the cam rotates through the remaining 30°, when the same 




MACHINE DRAWING 



103 



cycle of movement is to be repeated as long as desired. This is 

briefly expressed as follows: 

Harmonic rise 120° 

Rest 60° 

Uniformly accelerated and retarded fall 150° 

Rest.. 30° 

1. Follower Positions. The length of travel Ae being known, 

it is divided for purposes of the rise, by the principles of Fig. 88, into 




Fig. 90. Diagram of Complex Motion Plate Cam 

distances giving harmonic motion of the follower; and for purposes 
of the fall, by the principles of Fig. 89, into distances giving uniformly 
accelerated and retarded motion. Eight spaces are chosen, so that 
the process of making these divisions is an exact repetition of the 
method in Figs 88 and 89. 



104 MACHINE DRAWING 

2. Cam Radii. The diameter of the base circle being chosen, 
and, for the purpose of this problem, the center being assumed in 
line with the path of the follower, draw the original radius CA, 
then the radii CX, CZ, and CW, limiting the arcs of rise, rest, and 
fall respectively. As 8 divisions of the follower path have been 
chosen, the arcs of rise and rest must each be divided into 8 equal 
divisions. It should be observed that while the divisions are equal 
throughout each arc, the arc of fall being different from the arc of 
rise, the divisions of the arc of fall are not equal to the divisions of the 
arc of rise, measured on the base circle. 

3. Follower Rotation. The rotation of the follower about the 
cam, for the period of rise, is accomplished by striking arcs through 
the points 1,2,3, 4, 5, 6, 7, and e, making the intersections R v R 2 , R 3 , 
R 4 , R 5 , R Q , R 7 , and R 8 , with the cam radii. The rotation of the fol- 
lower about the cam, for the period of fall, is accomplished by striking 
arcs through points V, 2', 3', 4', 5', 6', T ', and e, making the inter- 
sections F lf F 2 , F 3 , F 4 , F 5 , F Q , F 7 , and F 8 , with the cam radii. These 
points of intersection represent the centers of the follower roll in its 
rotated positions, and from these centers should be struck arcs with 
a radius equal to the radius of the follower roll. 

4. Tangent Line. A smooth curve is now drawn tangent to 
these small arcs, thus forming the outline of the cam. 

5. Testing. The cam may be tested by the tracing-cloth 
method, precisely as in the cases already developed. 

6. Pressure Lines. The pressure lines are found in exactly 
the same manner as in Fig. 81, and can be rotated back to the points 
in the path of the follower, in order to conveniently study the change 
in direction of the pressure lines as the follower moves along its path. 

It should be noted that in Fig. 90 the same method of procedure 
is followed as in Figs. 79 to 86, except that the determined points in 
the path of the follower do not make equal divisions of the path, 
as in the case of uniform motion. 

Translation Cams 

Rotating plate cams, like those thus far considered, are most 
commonly met with in practice. A straight-line, reciprocating 
motion of a plate, however, may be made to produce similar follower 
movements, in which case the cam is known as a translation cam. 
A straight-line movement is equivalent to movement along an arc 



MACHINE DRAWING 



105 



with infinite radius. With this understanding, the same principles 
may be made to apply to translation cams as to rotating cams. 

Development of Translation Cam. Suppose it is required to 
produce the same movement of the follower as in Fig. 90, by means 
of moving a plate in a straight line instead of rotating it. This case 
is shown in Fig. 91. 

1. Folloiver Positions. The same follower motion being 
required as in Fig. 90, the path is laid out exactly in the same way, 
the follower positions for the rise along path D8 fulfilling the require- 
ment of harmonic motion, and for the fall along path IF 8 , fulfilling 
the requirements of uniformly accelerated and retarded motion. 
This is shown in the figure, and it is observed that no change from 
the method of Fig. 90 is employed. 

2. Cam Radii. The base circle does not exist in this case as 
a circle, but has become a straight line, and may be chosen of any 
length, say Dx. The cam radii, being always perpendicular to the 



/' m' it p' r s- t' u' \/' x' 




Fig. 91. Diagram Showing Development o f Translation Cam 



cam arc (in this case the straight line Dx), become parallel lines, 
perpendicular to Dx. The cam arc of rise in Fig. 90 is now repre- 
sented in Fig. 91 by the distance D8, which should fulfill the relation 

tT- = t^k ; in order to make the same relative movement of cam dur- 
Dx 3o0 

ing rise as in Fig. 90, Dk should likewise be divided into 8 equal parts. 

The arc of rest in Fig. 90, being J the arc of rise, the distance kl in 

Fig. 91 is made J the distance Dk. The arc of fall in Fig. 90 being 

1J the arc of rise, the distance Iv in Fig. 91 is made 1\ the distance 

Dk. The final arc of rest in Fig. 90 being \ the first arc of rest, the 

distance v x in Fig. 91 is made \ the distance kl. This completes the 

cycle; and the parallel lines aa', bb', cc', etc., drawn through the 



106 MACHINE DRAWING 

several points of division as noted, represent the several positions 
of the cam radii. 

3. Folloicer Rotation. Since the lines of follower rotation are 
all perpendicular to the cam radii — which in this case are all parallel — 
the rotation, or translation, of the follower is accomplished by draw- 
ing parallel lines through the determined points of the path, pro- 
ducing the intersections R v R 2 , R 3 , R v etc. Between points R 8 and 
F 8 , the follower rests; and for the period *of fall, the intersections 
F 8 , F 7 , F Q , F 5 , etc., are determined as for the rise, by producing the 
parallel lines through the points in the path of fall. From point v to 
x the follower again rests. These intersections represent the centers 
of the follower in its translated positions. 

Now, with a radius equal to the radius of the follower roll, arcs 
are struck to represent the outline of the follower in each of its trans- 
lated positions. 

4. Tangent Line. A smooth curve is now drawn tangent to the 
several translated positions of the follower roll. In this cam a new 
feature is introduced by drawing these tangent lines on both sides 
of the roll, thus making a groove which holds the follower firmly 
in position at all times. This gives an absolutely positive fall to the 
follower roll. The same grooved construction might have been made 
on any of the cams heretofore studied, instead of allowing the fol- 
lower to come down by gravity or by the force of a spring. 

5. Testing. The cam may be tested by the tracing-cloth 
method as before, the procedure in this case, however, being one of 
translation instead of rotation.- The original radius, with the fol- 
lower in its several positions being traced upon the cloth, is set upon 
each of its translated positions, and, by careful inspection, it is noted 
whether the roll, in this position, just touches the faces of the cam 
groove as drawn. 

6. Pressure Line. The pressure lines are drawn precisely as 
in all cases thus far considered, and may be translated back to the 
path of the follower in order to study their direction as the follower 
moves along its path. 

Although the same cycle of follower movement has been accom- 
plished in this case as in the rotating cam, Fig. 90, the. translation 
cam is not in position to begin a repetition of the cycle by further 
movement. If we reversed the motion of the cam, the cycle also 



MACHINE DRAWING 



107 



would be reversed; and in the cam under discussion we should have 
a rest, then a uniformly accelerated and retarded rise, then a rest, 
then a harmonic fall, the periods of time being reversed as well as the 
motion. We could, of course, by choosing the motion for rise and 
fall exactly the same, secure the same motion for the reversed as for 
the forward movement of the cam. 

Cylindrical Cams 
Development of Cylinder Cams. Suppose that the outline of 
the translation cam as developed in Fig. 91 be wrapped around a 
cylinder whose circumference is exactly equal to Dx, and that the 
lines represent a spiral groove cut into the surface of the cylinder. 
If, then, a follower roll be allowed to remain in this groove while the 



■WIDTH OF PLATE=LCn6TH OFCYL 




Fig. 92. Development of Cylindrical Cam 

cylinder is rotated on its axis, the cycle of follower movement will be 
repeated as long as we choose to rotate the cylinder. Such a grooved 
cylinder is known as a cylindrical cam. 

Fig. 92 shows a cylindrical cam in two projections. Attention 
is called to the tapering follower roll used. This is because it is 
necessary that points on the sides of the groove and the surface of 
the roll have the same velocity about the center C. The roll, there- 
fore, must be the frustum of a cone whose apex is at C. 

The top of this groove is produced by wrapping Fig. 91 around 
the surface of the cylinder as previously described. The bottom of 
the groove is produced by making a translation cam whose base line 
is equal in length to the circumference of the cylinder at the bottom- 



108 



MACHINE DRAWING 



of the groove, and then wrapping it around that cylinder. This 
base line for this smaller cylinder is divided into the same number 
of parts as the line Dx, the divisions, however, all being proportionally 
smaller. The length of the follower path, and its divisions, are in 
.nowise different from those shown in Fig. 91; and the method of 
developing the outline of the cam is precisely the same. 

The wrapping of these translation cams, for purposes of the 
drawing, is accomplished by means of dividers and compasses, 
according to the principles for the development of cylinders, as 
explained in Mechanical Drawing, Part III. 

The limitations of construction of cylindrical cams are consider- 
ably greater than those of the simpler rotating cams; and it is more 
frequently a question of experiment and trial to get the proper sur- 
faces, than it is of exact theoretical layout on the drawing board. 

BELTING 

Cams and gears transmit positive motion from the driver to the 
follower by direct contact of the surfaces. As the distance between 




Fig. 93. Diagram of Simple Open Belt Drive 



centers of shafts increases, the driver and follower for such methods 
of transmission become large, unwieldy, and costly, and rigid links 
may be used to connect the rotating pieces, as in the case of parallel 



MACHINE DRAWING 



109 



rods of a locomotive. For a further increase of distance, the trans- 
mission is attained by means of belts and pulleys, and, if the distance 
is very great, by wire ropes and sheaves. As there is always some 
slipping of the belt (from 1 to 2 per cent), the velocity ratio is not 
exact; but this is not essential in many classes of machinery. The 
slip and stretch of the belt reduce the shock when heavy machinery 
is set in motion — an important feature in many cases. 

Open and Crossed Belts. The simplest forms of belt drives 
are the open belt (Fig. 93) and the crossed belt (Fig. 94). In each 




Fig. 94. Diagram of Simple Crossed Belt Drive 



case the shafts are parallel, and the pulleys fastened to the shaft with 
set screws or keys. The central planes of the pulleys must obviously 
be coincident. The belt is then tightly stretched over the pulleys, 
and, assuming B, the driver, to turn in the direction of the arrow, 
motion will be transmitted to A, on account of the friction set up 
between the belt and pulley surfaces. The fibers of the belt, in 
running on or off the pulley, bend over one another, so that those 
next the pulley, on the inside of the belt, are compressed, while those 
on the outside are stretched. Assuming the compression and stretch 
to be equal, then the central fiber does not change in length. This 
central fiber is shown in the figure by a "dash-and-dot" line. Con- 
sidering that there is no slip of the belt on the pulley, the face of each 



110 MACHINE DRAWING 

pulley will move exactly with the belt, and the turns of each pulley 
will depend on its circumference; or, 

t f a - Speed of belt S 

"Circumference of A 7TX Diameter of A 

m „ „ Speed of belt S 

Turns of B = 



Circumference of B ir X Diameter of B 

. . . Turns of A Diameter of B 

e oci y ra 1 — ip urng f j5 _ Di ame ter of A 

Thus the velocity of the shafts is inversely proportional to the ratio 

of the diameters of the pulleys. The action of the belt in bending 

about its central fiber has the effect of increasing the diameter of the 

pulley by an amount equal to the thickness of the belt, and an exact 

calculation for velocity ratio must take this fact into consideration. 

For example, suppose that the diameters of A and B are 8" and 24" 

respectively, and that the belt is \" thick. Then the velocity ratio 

24 ' 24.25 

is -5- = 3 for the usual approximate calculation; but Q * =2.939 

for the exact value. 

The direction of shaft rotation depends on the method of apply- 
ing the belt. In the case of the open belt, the top surfaces of each 
pulley being connected, each shaft rotates in the same direction; 
while in the case of the crossed belt, the top surface of A being 
connected to the bottom surface of B, the shafts rotate in opposite 
directions. Thus the directions of rotation are the same when the 
center line of belt lies wholly on one side of the line connecting the 
centers of pulleys; and different when it intersects the line of centers. 

Crowning Pulleys. Suppose that a flat belt is placed on the side 
of a double cone, Fig. 95, and that we start to rotate the cone in the 
direction of the arrow. The edge E, which is stretched more tightly 
than F, has a greater grip on the surface of the cone, and will climb 
up the incline as shown by the dotted lines. With continued rotation 
of the cone, the belt, if not prevented, will move farther up the 
incline, will finally pass the crest, and start down on the other side 
until the two edges E and F have equal tension, or the pull to the 
right is balanced by an equal pull to the left. The center line of the 
belt will now run in the central plane X Y of the pulley. 

As long as this condition is maintained, the belt will run true 
and will stay on the pulley. Also, if the pulley faces were perfectly 



MACHINE DRAWING 



111 



flat, the belt a perfectly homogeneous piece of leather, and the shafts 
perfectly parallel, the belt would stay in the pulley. Such perfect 
conditions, however, cannot be produced or maintained, and it is 
therefore necessary in practice to imitate the conditions of Fig. 95, 
and "crown" either one or both pulleys, so that the belt will not 
develop any tendency to run off. On the contrary, it will constantly 
seek to keep its center line in the central plane of the pulleys, any 
tendency of one edge to slacken and run off being instantly counter- 
acted by the tightening up of the other as it starts to climb, thus 
pulling the belt back until the balance is secured. A very slight 
amount of crowning will accomplish this result, and as little crown 
as possible, consistent with good running, should be provided, 
that too great inequality 6f tension in the belt may not be intro- 
duced. 

In Fig. 93, if the shafting be not parallel, 
the center line of the belt will not run in the 
central plane of the pulley, and the belt will 
climb towards the high part of the pulley, as in 
the above case of the cone, and we may expect 
the belt to run off. 

The above discussion reduces to one funda- 
mental working condition for belt transmission, 
viz, The center line of the belt leaving a pulley 
must lie in the central plane of the pulley to tvhich 
the belt is delivered. 

This principle is applicable to all cases of 
belt transmission, however complicated, whether 
the shafts be parallel or at an angle. The use of guide pulleys is 
merely a means of controlling the delivery of the belt according to 
the principle. The student should commit this principle to memory, 
and go over its application until he is sure that he understands it; 
for without it he cannot solve complicated belt problems, and he 
cannot feel sure of his solution of even the simplest ones. In the 
pages of discussion and illustration which follow, the student should 
constantly note the recurrence and application of this principle, as 
it is really all there is to the solution of belt problems, except familiar 
knowledge of how to make the drawing projections, which he already 
is supposed to possess. 




Fig 95. Theory of 
Crowning a Pulley 



112 



MACHINE DRAWING 



Tight and Loose Pulleys. Tight and loose pulleys are provided 
for cases in which a machine is to be thrown in and out of service 
without stopping the driving shaft. 

A common arrangement is shown in Fig. 96, where a pulley 
with a straight face is located on the line shaft, and two pulleys with 
crowned faces are on the countershaft. Pulley B is loose on the 
shaft, and C is fast to the shaft. A collar D is placed on left of B, 
to prevent its end motion. Shifting the belt is accomplished by 
pushing on the advancing side of belt, close to the receiving pulley. 




Fig. 96. Diagram of Tight and Loose Pulley Drive 

The shifter F has two iron pegs, one on each side of the belt, and 
is operated by hand. The belt is readily guided by pressure on 
the advancing side, for the motion of the receiving pulley aids the 
motion of the belt; but if pressure were applied to the retreating 
side it would be necessary to use enough force to shift the belt bodily 
sidewise on the face of the pulley. As excessive tension on the belt 
decreases its life, the diameter of the loose pulley is often slightly de- 
creased, thus permitting the belt, when doing no useful work, to be 
under less tension than when driving. 



MACHINE DRAWING 



113 



^T 



t 




Another arrangement is to provide a clutch to throw into a loose 
pulley on the line shaft, the belt standing idle when not in service. 

Shafts Not Parallel. 
Suppose an open belt to 
connect pulleys A and B v 
on parallel shafts, Fig. 97. 

Draw a tangent XY 
to the pitch circles of the 
pulleys at the points L t and 
L 2 , where the belt leaves 
the pulleys. Now rotate 
the central plane of the 
pulley B v about ZFasan 
axis, through any angle C, 
to position shown by pul- 
ley B. The central planes 
(shaded) of pulleys A and 
B intersect on the line X Y, 
called the trace of the 
planes. The axes are now 
not parallel, but the belt 
may be made to run in one 
direction, for it still obeys 
the general principle of the 
guiding of belts; i.e., the 
center line of the belt, on 
leaving the driving pulley, 
is delivered into the cen- 
tral plane of the receiving 
pulley. 

Examining the figure, 
we find that the center line 
of the belt moves in direc- 
tion of arrow from L t to 
R, and around pulley B to L 2 , from L 2 on the surface of B to R 2 , 
thence on surface of A to L v the starting point. From the point 
L v where the belt leaves A, until it reaches R, the center line 
of the belt is in the central plane of, the receiving pulley B, and the 




Fig. 97. 



Diagram of Pulley Drive where Shafts 
Are not Parallel 



114 



MACHINE DRAWING 




belt twists about this line, presenting a flat side to the face of pulley 
B at R. 

From L 2 , where the belt leaves B, until it reaches R 2 , the center 
line of the belt is continually in the central plane of the receiving 
pulley A, and a similar twist in the belt takes place. If now we 
attempt to reverse the direction of motion of the belt, the top of 
pulley A, moving in the direction of the dotted arrow, would carry 
point D of the center line of belt to the left-hand edge of A, as indi- 
cated by the dotted line DE, where it would drop off. Therefore, 
this belt drive for shafts not parallel is suitable 
only for motion in one direction. 

Quarter=Twist Belt. By rotating the cen- 
tral plane of B, Fig. 97, until the angle C be- 
comes 90°, a quarter-twist, or half-crossed belt, 
Fig. 98, is obtained; and if 
angle C becomes 180°, the 
crossed belt of Fig. 94 is the 
result. 

If the thickness of belt is 
neglected, it will be noted 
that the central plane of B 
(Fig. 98), which is represented 
by the trace XY, is tangent 
to the surface of pulley A; 
and similarly on the side view, 
the trace ST of the central 
plane of A is tangent to the 
surface of B. Now follow the 
center line of belt in the direc- 
tion of the arrows on the 
front and side views, starting at point A, where the belt leaves 
the upper pulley. From A to Z), and around to the back of pulley 
B, the center line is shown in the trace X Y of the front view. From 
B, where the belt leaves the lower pulley, to c, and around to the 
front and starting point A, the center line is shown in the trace 
ST of side view. Therefore the center line of the belt is always 
delivered into the central plane of the receiving pulley, and it will 
drive satisfactorily in the direction of the arrows. Reversing 



Fig. 98. Diagram for Quarter-Twist Belt 



MACHINE DRAWING 115 

the motion will cause the belt to run off the pulleys, as in the pre- 
vious case. 

The belt should always be put on so that the same <nde of the belt 
touches both pulleys when it is possible to do so. In making the 
drawing of the belt we shall call the side of the belt which touches the 
pulleys the inside, and the other side the outside. Now, referring 
first to the left-hand elevation in Fig. 98, where the belt lies around 
the circumference of the upper pulley, from the point c, where the 
upward-moving part of the belt strikes the pulley, around to A, where 
the downward-moving part leaves the pulley, only the edge of the 
belt is visible, and is represented by drawing an arc of a circle from 
line oc around to oA, with a radius equal to the radius of the pulley 
plus the thickness of the belt. The location of c may be found 
closely enough for all practical purposes, by drawing a line from B 
tangent to the upper pulley, c being the point of tangency, and oc 
the radius drawn through c. In drawing the arc of the circle from 
octo oA, it is well to let it run by these lines a little way in the pencil 
drawing, and that part which is not used may be erased after the 
drawing is inked. The descending part of the belt leaves the pulley 
at A; and from that point to the place where it strikes the lower 
pulley, it twists through an angle of 90°, coming out over the front 
of the lower pulley. The edge of the belt, which we see in its full 
thickness where it leaves the upper pulley at A, twists toward the 
left, less and less of it being seen as the belt descends, until at d, 
where it strikes the other pulley, the two corners of this edge coin- 
cide, and from there to the bottom of the pulley we see this edge 
of the belt as a line. At the same time that the thickness of the 
belt has been disappearing from view, the outside of the belt has been 
coming into view, until at dd' we see the full width of the belt, the 
outside corner being the one which is visible. The inside corner 
is behind the rest of the belt, and while it may be shown dotted in 
the drawing, it is usually omitted entirely. From d' to the bottom 
of the pulley the two right-hand corners coincide. Points d and d' 
are found by drawing the horizontal dotted line through D (side 
view), and laying off on this line a distance equal to one-half the 
width of the belt each side of line XY. From ee' the belt goes 
around the back side of the pulley to W, where it begins to be 
drawn off to the left, bb f being on the center line drawn through 



116 



MACHINE DRAWING 



the shaft, since, by glancing at the right-hand view, we can see that 
the upward-moving part of the belt leaves the lower pulley at B, 
which is on a level with the center of the shaft. After leaving W, 
the belt remains behind the pulley for a short distance, and is shown 
dotted. It is projected at its full width at bb f , but as soon as it 
leaves the pulley it begins to twist toward the right, the left-hand 
edge gradually coming into view until it is seen at its full thickness 
where it strikes the pulley at C. At the same time, the inside face 
of the belt, which is toward the front when the belt leaves the pulley, 
gradually turns toward the right, and appears 
narrower until it disappears from view — that is, 
projected as a line. This completes the front 
view, and the side view is drawn according to 
the same principles, as is also the plan view. 

To be strictly correct, 
the sides of the belt should 
be shown curved at A and 
B, for the belt is pliable 
and starts to curl and slip 
sidewise a short distance 
above these points. In 
order not to have an exces- 
sive side slip, the angles 
c B A and DAB should 
not be more than 25°. 

Figs. 99 and 100 show 
what changes are made in 
the location of the pulleys 
and the appearance of the 
belt by changing the direction of rotation of the shafts. In Fig. 99 
the lower shaft turns in the same direction as in Fig. 98, but the 
upper shaft turns in the opposite direction. In Fig. 100 the upper 
shaft turns in the same direction as in Fig. 98, and the lower shaft 
turns in the opposite direction. 

Reversible Quarter=Twist. Two Guide-Pulleys. In order to 
reverse a quarter-twist belt, it will be necessary to introduce one 
or two guide-pulleys to bring the center line of the belt at all times 
into the central plane of the receiving pulley. Fig. 101 shows an 




Fig. 99. First Variation from Fig. 93 for Quarter- 
Twist Belt 



MACHINE DRAWING 



117 



arrangement where two guide-pulleys are used. Let the driving 
pulley R and the driven pulley P be located as in the case of the 
quarter-twist belt of Fig. 99. Suppose that the direction of rotation 
is but seldom reversed, and that the usual motion of the driver is 
in the direction of the arrow. The part of the belt which has the 
greater load should have a direct connection between R and P, 
leaving the slack side to run over the guide-pulleys, thereby decreas- 
ing the stress on the belt and lessening the fric- 
tion in the journals of the guide-pulleys. 

Receiving point A is then connected to B, 
the point of departure from the back of the 
driven pulley, instead of over to the front face, 
as in case of Fig. 99; and the 
belt twists about this line as 
an axis through an angle of 
90°, so as to present flat sides 
to both pulleys. The plan 
view of the center line of the 
belt is the line of intersection 
AB of the traces of the cen- 
tral planes of R and P. Evi- 
dently the belt will run in 
either direction along the 
trace of either plane. From 
the point of departure D of 
the driving pulley, the belt 

trter- must be led to the receiving 
Twist Beit point E of the driven pulley, 

by means of guide-pulleys. Draw BE for the plan view of the 
central plane of the guide-pulleys. This plane is perpendicular to 
the paper, and its traces or intersections with the central planes of 
R and P are shown in X Y and DH of the front view. 

The guide-pulleys are idlers introduced only to form a path 
for the belt, and do not in any way affect the velocity ratio. They 
may, therefore, be made of any convenient size to suit the existing 
conditions. We may then assume on the plan view, that J and K 
are points on the axes of the pulleys M and N, and draw the guide- 
pulleys so that the face of M bisects the front face of P at E, and 




118 



MACHINE DRAWING 



one face of N bisects the right-hand face of R at D. On the front 
and side views, the location of the axes has been assumed as GG and 

FF, and the corresponding views 
of the pulleys are drawn according 
to the principles of projection. 

Examining the belt in passing 
from D to E, we find its center 
line goes from D in the central 
plane of R, to H in central plane 
of N, around N and M, which 





Fig. 101. Reversible Quarter-Twist — Two-Guide Pulleys 



have one common central plane, arriving at C, a point in the 
trace of the central planes of M and P, and from leaving point C 
to receiving point E. It will be noted that the center line of belt 
connecting both leaving and receiving points is always in the cen- 
tral planes of both pulleys, and, therefore, the direction of motion 
may be reversed at will. If the belt be followed around the pul- 



MACHINE DRAWING 119 

leys, we find both sides of the belt come, successively, in contact 
with the pulleys. Therefore, the belt must be given a single twist 
before uniting the ends together. 

It is usually desirable to have only one side the working side; 
but if such were the case in this arrangement of pulleys, it would 
bring a sharp twist in the belt, between M and A T , which might be 
a greater objection. 

One Guide- Pulley * Fig. 102 shows the arrangement of the 
pulleys for the belt to run in either direction, using only one guide- 
pulley. The ordinary direction of rotation is that shown by the 
arrows. The upper pulley is the driver, and, as in the case where 
two guide-pulleys are used, the tight part of the belt goes directly 
from one main pulley to the other, the slack part of the belt returning 
over the guide-pulley. The shaft of the guide-pulley must be set 
at an angle with both main shafts in order to guide the belt properly. 
The method of locating the main pulleys is exactly the same as in 
the case where the two guide-pulleys are used, so that the explanation 
given for that case will apply here, and all we need to consider in 
this case is the location and drawing of the guide-pulley. 

We shall first consider the two elevations. The plumb line 
X Y, as well as being the center line of the tight part of the belt, is 
the line of intersection of the central planes of the two main pulleys. 
Choose a point in the line X 7, which may be anywhere along the 
line, depending on how far the guide-pulley is to be from one or 
the other of the main shafts, but preferably about half-way between 
them. The point is marked M h in the left-hand elevation, and 
M v in the right-hand elevation. From M h draw a line tangent to 
the upper pulley at D h , and from M\ draw a tangent to the lower 
pulley at E\ The other projection of the line M h D h will be M V D\ 
coinciding with X Y in the right-hand elevation; and the other pro- 
jection of M V E V will be M h E h , coinciding with XY in the left-hand 
elevation. W T e now have two lines, MB and ME (shown respectively 
by their two projections, M v D v —M h D h and M v E v —M h E h ), which 
determine the plane of the guide-pulley and which are practically 
the center lines of that part of the belt which passes over the guide- 
pulley, and our problem is one of projections. The problem is to 



*This section is optional. 



120 



MACHINE DRAWING 



find on the drawing paper the traces of the plane which contains the 
two lines, which is the central plane of the guide-pulley, and revolve 




Fig. 102. Reversible Quarter-Twist — One Guide Pulley 



this plane about one of its traces until it is parallel to the plane of 
the paper, so that the true angle between the lines will be shown; 



MACHINE DRAWING 121 

then draw the guide-pulley tangent to the lines in their revolved 
position, and revolve the lines back to their former position, revolv- 
ing the guide-pulley back at the same time. To carry out this 
construction, proceed as follows: Draw a ground line anywhere 
between the two elevations, parallel to X Y ; and, for the time being, 
consider one of the elevations as a horizontal projection and the other 
as a vertical projection, remembering that our drawing is made as 
if projected on two planes located as in Fig. 2, Machine Drawing, 
Part I, or, as it is commonly expressed, "in the third quadrant". 
We shall treat the left-hand elevation as if it were the horizontal 
projection, and the right-hand elevation as if it were the vertical 
projection. Extend line M h B h until it meets the ground line at 
d h ; and at d h draw a perpendicular to the ground line, meeting XY 
(which is the same as M V D V extended) at d v . Through d v draw a 
line parallel to M V E V ; and this line, which is marked VP, is the 
vertical trace of the plane which contains the lines MB and ME. In 
like manner find the horizontal trace by extending M V E V to meet the 
ground line at e v , erecting a perpendicular at e v to meet M h E h at e h , 
and drawing HP through e h parallel to M h D h . If the work is cor- 
rectly done, HP, VP, and the ground line will intersect in a common 
point. Now through M h draw a line perpendicular to HP, meeting 
HP at p. Construct the right triangle tm h P (Fig. 103), making m h P 
equal to M h p on Fig. 102, and making m h t equal to the perpendicular 
distance of M° from the ground line in Fig. 102 (that is, equal to 
cM v J. Then take the distance Pt (Fig. 103) and lay it off on the 
line pM h (Fig. 102) from p, thus obtaining point N. Join N and 
e h , and through N draw Ng parallel to M h D h . The lines Ne h and 
Ng are the projections on the horizontal plane of lines ME and MB, 
respectively, when the plane P, which contains these two lines, is 
revolved so that it is parallel to the horizontal plane. Therefore 
the angle g Ne h is the true size of the angle between lines ME and 
MB. Now, with a radius equal to the radius of the guide-pulley 
which is to be used, draw a circle which shall be tangent to the lines 
Ne h and Ng. This circle is the central circle of the guide-pulley 
revolved parallel to the horizontal plane, and its center S is the 
revolved position of the center point of the guide-pulley, and, of 
course, lies in the plane P. To revolve the central circle of the guide- 
pulley back so as to get its two projections when it is in the position 



122 MACHINE DRAWING 

which it actually occupies with relation to the two main pulleys, 
we shall first revolve the point S back to h . To do this, draw SK 
perpendicular to HP. Then in Fig. 103, lay off from P along the 
line Pt the distance PV, equal to SK in Fig. 102. Care must be 
taken to lay off this distance from P rather than from t; and in 
order to remember from which point to measure, the student can 
bear in mind that distances measured along the hypotenuse from 
P (Fig. 103) represent distances measured from HP (Fig. 102). 
Having thus found point V, draw a line perpendicular to 
m h P, meeting it in o h ; take distance o h P in the dividers, and 
lay it off from K along KS (Fig. 102), thus getting O h . 
Then point O h will be the center of the ellipse which repre- 
sents the center circle of the guide-pulley in its actual 
position. Point 2, where KS cuts M h D h , will 
be one end of the the minor axis, and point 1 , 
found by laying off h l equal to O h 2, will be 
the other end of the minor axis. The major 
axis is found by drawing a line through O h 
parallel to M h D h , and laying off along this line 
^iaSLSMg^ 11 from h the distances h 3 and 0% each equal 
to the radius of the guide-pulley. Having now 
found the two axes of the center ellipse, it can be drawn by any 
geometric method for constructing an ellipse. 

We shall next find O v by prolonging the major axis of the ellipse 
just found until it meets the ground line at o 2 , then erecting a per- 
pendicular to the ground line at o 2 to meet VP at o 3 , drawing a line 
through o 3 , parallel to the ground line, and from h drawing a line 
perpendicular to the ground line which will meet the parallel through 
o 3 at O v . This point will be the vertical projection of the center 
of the middle circle of the guide-pulley. The ellipse, which is the 
vertical projection of this middle circle, is found from V in a way 
exactly similar to that in which the ellipse for the horizontal pro- 
jection was found from h . 

The next step is to draw the guide-pulley and its shaft, and 
to do this we shall revolve the central ellipse over in each view in 
such a way that we shall have it projected as a line. We shall take 
the horizontal projection first. Extend the major axis of the ellipse 
from h to o 4 , making h o* equal to the perpendicular distance of 




MACHINE DRAWING 123 

0° from the ground line. Draw 0*1 through point 1 parallel to 
h o A . With o 4 as a center, and with a radius equal to the radius of 
the guide-pulley, cut o G l at o 6 , and cut D h M h extended at o 5 . Points 
o 6 , o 4 , and o 5 will be in a straight line, and the line joining them will 
be the edge view of the central circle of the guide-pulley. About this 
line o 6 o 5 draw a rectangle as shown, the width of the rectangle being 
made equal to the width of the face of the guide-pulley. Through 
o 4 draw a line perpendicular to o 6 o 5 , which will be the revolved posi- 
tion of the center line of the guide-pulley shaft. The method of 
revolving back to get the axes of the ellipses, which are the projec- 
tions of the edges of the pulley in its actual position, and to get 
the projection of the shaft, will be clear from a careful study of 
the figure. 

The vertical projection of the guide-pulley is found by revolv- 
ing over in exactly the same way, the distance v o 7 being equal to 
the perpendicular distance of h from the ground line. It is well 
to assume a definite length for the shaft, whether this be the actual 
length which the shaft would have or not. The length assumed 
in the figure is T X T 2 (same as T Z T A ), and half of this is laid off 
each side of o 4 in the revolved horizontal projection. 

This completes the two elevations of the guide-pulley. The 
plan is drawn as follows: Find the projection LL of the two ends 
of the shaft as shown by the construction lines; then revolve over 
by drawing line KK 1 at any convenient place parallel to LL, draw- 
ing perpendiculars through the points LL, meeting the parallel line 
at K and K 1 , and laying off on these perpendiculars the distances 
E}L X and KL\ equal respectively to L D P D and L E P E in the ele- 
vation. The line L X L 2 , joining the points L 1 and L 2 thus found, 
is the revolved position of the shaft, and should be equal in length 
to T X T and ff in the elevations. 

We can now draw the rectangle which represents the 
revolved position of the guide-pulley at the middle of the 
line L 1 L 2 , and find the ellipses from this rectangle in the same 
way as we found the ellipses from the rectangle in the other two 
views. 

The belt is drawn in accordance with the same kind of reasoning 
as was used in determining the way the belt would look in the other 
kinds of quarter-twist belts which we have studied. 



124 



MACHINE DRAWING 



«u 



Belts Connecting Shafts in Same Plane But Not Parallel. It 

very often happens that a belt must connect two shafts which are 
on the same level, but which are not parallel. The connection 
can be made, whatever the angle between the shafts, by the use of 
two guide-pulleys. If the two main-shaft pulleys are of the same 
diameter, the belt may be made to run in either direction by putting 
both guide-pulleys — or mule pulleys, as they are often called — on 
the same shaft, which will be perpendicular to the plane containing 
the axes of the main shafts. That is, if the main 
shafts are horizontal, the shaft for the guide-pulleys 
will be vertical. If the main pulleys are of different 
diameters, the guide-pulleys may still be placed on 
the same vertical shaft, but in this case the belt can 
run in only one direction. If the belt is to run in 
either direction, the guide-pulleys are placed on sepa- 
rate shafts, which are usu- 
ally adjustable in position, 
so that they may be tipped 
at the proper angle to re- 
ceive and deliver the belt. 

We shall first take the 
case where the two main 
pulleys are of the same 
size. Fig. 104 shows the 
arrangement, the upper 
view being the plan, and the 
lower view, the elevation. 
R and S are the two main 
pulleys, and C and D are 
the two guide-pulleys. The 
line X Y is the line of inter- 
section of the planes of the main pulleys. The location of the 
guide-pulleys is sufficiently clear from the drawing, without further 
explanation. 

Fig. 105 shows the arrangement when the main pulleys are of 
different diameters. Here the pulleys can turn only in the direction 
shown by the arrows; for if the direction were reversed, the belt 
would leave the pulleys. The pulleys in plan appear the same as 





Fig. 104. 



Belt Drive for Same Sized Pulleys, Shafts 
not Parallel but in Same Plane. 



MACHINE DRAWING 



125 



f-4- 




in Fig. 104. In the elevation, the upper guide-pulley, which receives 
the belt from S, has its central plane tangent to the pulley S at the 
point where the belt leaves S, as shown by the line A V B V . The 
lower guide-pulley, which receives the belt from i?, has its center 
plane tangent to R, as shown by C V D V . If the pulleys were to turn 
in the opposite direction, the upper guide-pulley would have its 
plane tangent to R, and the lower one, its plane tangent to S. 

Cone Pulleys. It is often necessary to provide a range of speed 
variation in a shaft belted from a line shaft running 
at a constant rate. A familiar case of this kind is 
the ordinary lathe spindle. This may be done by 
shifting the belt from end to end of either a pair of 
cones or conoids, Fig. 106, depending on whether the 
belt is crossed or open. To work satisfactorily, a 
shipper must be located at each cone or conoid to 

guide the belt; otherwise it 
may climb. As these ship- 
pers give trouble and wear 
the belt, and the belt itself 
is unequally stretched, it 
is usual to approximate the 
conoids by stepped cones, 
or cone pulleys. In order 
to have t the belt equally 
tight for each pair of steps, 
the diameters of the steps 
must be so proportioned 
that the length of belt re- 
mains constant. 
It can be shown, geometrically, that for a crossed belt this 
condition is obtained when the sum of the diameters of each 
pair of steps is constant. In Fig. 106, a three-step cone with crossed 
belt is shown; and, adding together the diameters of the pair of steps 
connected by the belt, we have 11+6 = 17 for the constant of this 
cone pulley. 

For an open belt, an extended calculation is necessary for 
diameters giving a constant belt length, and a simple graphic 
method for laying out the cones has been published by Mr. C. A. 




Fig. 105. 



Belt Drive with Main Pulleys of Different 
Diameters 



126 



MACHINE DRAWING 



Smith in "Transactions of the American Society of Mechanical 
Engineers" (Vol. 10, p. 269). Here the distance between shafts and 
diameters for one cone pulley is assumed, or is known from the 
conditions of the drive. 

In Fig. 107, lay off AB equal to the distance between centers 
of shafts; and with these points as centers, draw circles C and D 
equal, respectively, to the maximum and minimum diameters of the 




Fig. 106. Cone Pulleys for Spindle and Countershaft 

given cone pulleys. Draw the belt line EF. From a point G, half- 
way between A and- B, erect GH perpendicular to AB, and make 
it equal to 3.1416 AB (for the sake of space, it is not drawn to this 
scale in the cut). With H as a center, draw a circle tangent to EF; 
then the belt line of any other pair of pulleys must be tangent to 
this latter circle. 

Assume B 1 the diameter of one of the pulleys, and draw a 
common tangent to circles D t and H, producing it past the center 
B. From B draw a perpendicular BF X to the common tangent; 
and with BF X as a radius, draw in the circle C v which will give 



MACHINE DRAWING 



127 



the pulley required to work with D v and having approximately the 
same length of belt as on pulleys D and C. Continue the process 
until the required number of steps have been obtained. It must be 
noted that the limit for which this construction can be used is 
reached when the belt angle K is equal to 18°. When the angle K 
is between 18° and 30°, proceed 
as follows: 

Locate another point J on 
the line GH so that the distance 
HJ is equal to .298^45; draw a 
tangent to circle H, making an 
angle of 18° with the line of cen- 
ters AB, and from point J draw 
an arc tangent to this tangent. 
Make all belt lines which are 
greater than 18° tangent to this 
arc. 

Belt Holes. Very often a 
belt has to pass through a floor 
or partition. The holes through 
which the belt runs should be 
large enough to be sure that the 
belt shall never strike the sides, 
but it is desirable that they 
should be no larger than is nec- 
essary to accomplish that result. 
Accordingly, the holes should be 
laid out so that they may be cut 
in the right place and at the 
proper angle. Figs. 108 to 110 
show the method of locating 

. ■■ ... a , -i a -i i o Fig. 107. Diagrammatic Layout for Cone Pulleys 

the position or the floor holes lor 

the various kinds of belts, the top only of the floor being shown. 
In Fig. 108 we have a common open belt. The circles repre- 
senting the pulleys are drawn, and the belt drawn around them. A 
short pitch line should be also drawn in each part of the belt 
where it passes through the floor. These parts of the pitch line are 
simply lines parallel to, and halfway between, the lines which repre- 




128 



MACHINE DRAWING 



sent the outer and inner faces of the belt. Next draw the. two 
rectangles which represent the plan view of the pulleys, and draw 
through them the center line RS. From the points E and H, where 
the pitch line intersects the line representing the top of the floor, 
draw perpendiculars to RS, meeting it in points F and G. F and G 
are the center points of the rectangles 1 2 3 If and 5 6 7 8, which 
form the outline of the belt holes on the surface of the floor. The 

long dimension of the rectangles will 
be parallel to the shafts on which the 
pulleys are located. After the belt 
holes are so found, the distances of 
their center lines to the right or left 
of the lines T and X, respectively 
(which are the center lines of the 
shafts), can be measured on the 
drawing, and the workman can mark 
them out on the floor by plumbing 
down (or up) from the shafts, getting 
ro JL°r-)£. j^_ the lines T and X on the floor di- 
rectly under or over the center of 
the shafts, and thus locating on the 
floor the points F and G, and conse- 
quently the belt holes, from the 
dimensions taken from the drawing. 
Fig. 109 shows how to draw 
the holes for a crossed belt. Draw 
the two views of the pulleys and the center lines AC and DB of the 
belt in the elevation; also the center line RS in the plan. It is well, 
also, to draw the belt complete in the elevation, as it makes it easier 
to determine which way the belt holes will slant. From points E 
and 11, where the center lines of the belt intersect the floor line, 
draw EL and HK perpendicular to RS, and meeting RS in F and 
G. The points F and G are the center points of the belt holes, and 
it only remains to determine the angles which the center lines of the 
holes make with T and X, respectively. These will be the same as 
the angles made with HK and EL. When the belt is leaving the 
pulley at A, a line drawn perpendicularly across to its inner face 
would occupy the position indicated by the dotted line aa! in plan; 




Fig. 108. Diagram Showing Method of 
Locating Belt Holes 



MACHINE DRAWING 



129 



and the belt, in passing from A to C, twists through an angle of 180°, 
and the line which was at aa' will occupy the position cc'. There- 
fore, when the belt has passed from A to H, it will have twisted 




Fig. 109. Diagram Showing Location of Holes for Crossed Belt 

through an angle which will bear the same relation to 180° that the 
distance AH bears to the distance AC. That is, if AH = \ of AC, 
the angle JGK is \ of 180°, or 45°. Whether the angle JGK shall 
be laid off to the right or to the left of line HK, must be reasoned 
out by considering which way the belt twists in passing A to C. The 
angle of the other belt hole (LFM) is determined in the same way. 



130 



MACHINE DRAWING 



Fig. 110 shows the method of finding the belt holes of a plain 
quarter-twist belt, similar to Fig. 98. The centers G and F in plan 
are found by projecting from the elevation, as shown by the con- 
struction lines. The angle which the center line of hole at G makes 
with the center line of the shaft, is found by dividing 90° in the ratio 
of the distances P and N. The angle of the center line of the belt 




Fig. 110. Locating Belt Holes for Quarter-Twist Drive 

hole at F with the center line of the shaft, is found in a similar 
manner, by dividing 90° in the ratio of the distance AEtoE C. It 
is usually sufficiently accurate, however, after having found the 
angle at G, to draw the center line of the other hole parallel to it. 



MACHINE DRAWING 131 

General Practice. Working Conditions. A belt drive is work- 
ing under the most favorable conditions when, though not pulled up 
excessively, the belt "hugs" the pulleys tightly and wraps a large 
proportion of their circumference. 

Slipping. In the case of two pulleys of different diameters, 
made of the same material, connected by a belt, the belt will slip 
first on the smaller pulley, partly because the wrap of the belt is less 
upon that one, partly because the belt does not "hug" so tightly, 
owing to the smaller radius of curvature to which the belt must be 
bent. Sometimes the smaller pulley is lagged with rubber or leather 
so as to give it increased grip on the belt, thus making up for the 
tendency to slip, due to its small diameter. 

Location of Slack in Belt. On an inclined or horizontal drive 
the slack side should be on top, and the tight or pulling side under- 
neath, as the weight and slackness of the belt will act together to 
cause it to sag and increase the wrap. It is a well known fact that 
the greater the arc of contact, the greater the driving force which 
may be obtained from the belt. 

Vertical Drives. Vertical drives should be avoided as much as 
possible, as here the weight of the belt is always tending to decrease 
the "hug" on the lower pulley. 

Diameters of Pulleys. Increasing the diameter of pulleys, the 
same linear speed of belt being maintained, does not increase the 
power transmitted, except by permitting the belt to "hug" the pul- 
leys more tightly; and the larger the pulleys, the better this condition 
becomes, providing we do not exceed a certain economic speed for 
the belt. Flexible link belting, made of small leather links joined 
together by steel wire, gives excellent results, especially when used 
on horizontal drives, but it is rather expensive to install. A pulley 
rim perforated with small holes, to prevent any air cushion beneath 
the belt, is another means of increasing the "hug." 

Belt Tighteners. Belt-adjusting devices are often provided for 
changing the distances between the pulleys, thus enabling the proper 
tightness to be always maintained. Motor and dynamo bases are 
provided with slides and set screws for such adjustment. 

A tightener pulley is often used to increase the wrap of the belt 
or maintain the proper tightness. This is an idler pulley, which is 
weighted, or adjusted by screws against the belt. While such a 



132 MACHINE DRAWING 

pulley is a very ready and simple means of accomplishing the purpose, 
yet it should be remembered that the shaft carrying it is subjected 
to heavy pressure in its bearings, due to the belt tension; and the 
friction of the drive is considerably increased thereby. Tightener 
pulleys are used only when specific conditions prevent the results 
from being otherwise secured. 

Stiffness of Belt. It is generally preferable to use belts of two 
or more thicknesses for the sake of side stiffness, and also in order 
that any local imperfections of the leather in one layer may be taken 
care of by the other. Where the belts are to be shifted laterally, 
stiffness is an important item. If too pliable a belt is used on cone 
pulleys, the edges are apt to curl up, and the belt tends to climb and 
chafe against the side of the step, twisting like a corkscrew, and 
sometimes jumping from one step to another. 

Distance Between Pulley Centers. A good distance between the 
centers of shafting for ordinary belt drives is from 20 to 25 feet. 
With greater distances, the belt is apt to flop and run in waves; 
while at a less distance, the necessary tightness of the belt results in 
undue stretching. In crossed belts, the above distances should be 
especially adhered to ; for, with a wide, stiff belt and a short distance 
between centers, there is an excessive amount of rubbing on the sides 
of the belt, as well as strain caused by the twisting. 

Crossing and Quarter- Twisting. It is well to use as few crossed 
and quarter-twist belts as conditions will permit. In quarter-twist 
belts, the side angle, where the belt leaves the pulley, should be kept 
under 25°, as considerable power is lost in side slipping. For the least 
distance between the shafts a safe value is obtained if the distance is 
made not less than 2\ times the diameter of the larger pulley. A 
narrow belt gives better results than a wide one, on twisted belting. 

GEARS 
General Theory of Gears. Fig. Ill represents a pair of disks 
fastened to shafts A and B, respectively, and touching at the point 
P. If these disks be pressed tightly against each other, sufficient 
friction will be produced between them to cause one to drive the 
other. The number of revolutions B would make in a given time, 
would be to the number of revolutions made by A as AP is to BP; or, 

Revolutions B _AP 
Revolutions A BP 




MACHINE DRAWING 133 

Such friction disks will transmit but very little power without slip- 
ping; and even when required to transmit small power, cannot be 
depended upon to drive positively, as the least wear or loss of adjust- 
ment is liable to make them slip. 
Hence teeth are provided on each 
disk, such that they will lock to- 
gether and make it sure that when 
one disk is rotated the other must 
move also, without regard to 
whether the disks are pressed tightly Fig . m . Diagram of Sk^iTcTear Prin- 
together or not. In fact, it is desir- cip e 

able that this side pressure be avoided, in order to prevent 
excessive friction in the bearings of shafts A and B. 

Any shapes whatsoever of teeth would answer, provided they 
interlocked, so far as positive driving is concerned. But in order 
that the revolutions of the shafts shall always be inversely as the contact 
radii, or 

Revolutions B _AP 

Revolutions A BP 

it can be shown by geometry that the common normal drawn through 
the point of contact of any pair of teeth must always pass through the 
point P. 

A pair of gears, therefore, may be considered to be based on 
two disks, touching as in Fig. Ill, and provided with teeth such that 
these two conditions are fulfilled : 

1. Positive driving at all times. 

2. The common normal through the point of contact of any 
pair of teeth always passing through the pitch point. 

Pitch Circles. The circles corresponding to the disks are known 
as pitch circles, their diameters pitch diameters, and the point of 
contact P the pitch point (see Fig. 112). The distance, measured 
radially, from the pitch circle to the top of the tooth is called the 
addendum; and the circle through the top of the tooth, the adden- 
dum circle. The distance, measured radially, from the pitch circle 
to the beginning of the fillet at the bottom of the tooth, is called the 
dedendum; and the circle through this point the dedendum circle. 
In order that the top of the tooth on one gear shall not strike the 
surface between the bottoms of the teeth on the other, a further 



134 



MACHINE DRAWING 



distance is allowed between the dedendum circle and the root circle, 
known as the clearance. The distance from the center of one tooth 
to the center of the next, measured on the pitch circle, is called the 
circular pitch, and is evidently equal to the circumference of the pitch 
circle divided by the number of teeth. 

In order to run together, two gears must have the same circular 
pitch. The number of teeth in a pair of gears is proportional to 
the circumference of the pitch circles, and therefore to the pitch 
diameters, or pitch radii. The speeds of the shafts carrying the 
gears, being inversely proportional to the diameters of the pitch 
circles, are also inversely proportional to the numbers of teeth. 




CENTER DISTANCE 




GEAR -A 
DRIVER 



,TCH ^ 



GEAR -B. 
DRIVEN 



Fig. 112. Layout for Pair of Gears, Showing Construction Features 

Circular and Diametral Pitches. Since the circular pitch is 
equal to the circumference of the pitch circle divided by the number 
of teeth, there is a fixed relation, for any given gear, between the 
pitch diameter and the number of teeth. This relation is known as 
diametral pitch. Diametral pitch is not a distance, like circular 
pitch, but is the number of teeth per inch of pitch diameter of the 
gear. For example, if the diameter of the pitch circle of a gear of 
60 teeth were 20'', the number of teeth per inch of diameter would be 
60 
20 



= 3, and the gear would be described as a "60-tooth,. 3 diametral- 



MACHINE DRAWING 135 

pitch gear". The product of the circular pitch times the diametral 
pitch, is always equal to the constant, 3.1416; that is, if we have one 
kind of pitch, and wish to change to the other, we divide 3.1416 by 
the given pitch. For example, 4 diametral pitch is equal to 

x -^-r — = .7854" circular pitch. Again, 2" circular pitch is equal to 

3 1416 

— '—~ — - = 1.57 diametral pitch. Note carefully that diametral pitch 

is not "inches", but number of teeth per inch of diameter. 

Diametral pitch is very convenient to use, as the calculation is 
simpler than with circular pitch, and the pitch diameters of the gears 
come in even figures, or in even fractions of the pitch. For machine- 
cut gears it is universal practice to use diametral pitch in the speci- 
fication. For cast gears, where the teeth are fashioned by the pattern 
maker, it is common to use circular pitch. 

The thickness of the tooth LM, Fig. 112, is practically the same 
as the space TL for machine-cut gears. For cast teeth, however, 
the tooth must be thinner than the space, to allow for the inaccuracies 
of the pattern and casting. This allowance measured on the pitch 
circle is called backlash. 

Discussion of Terms. These terms are illustrated in Fig. 112; 
also the common normal KP to a pair of teeth in contact. Gear A, 
being the driver in the direction shown, a pair of teeth are in contact 
at point K. The curves of the teeth being of the correct shape, if a 
common tangent be drawn, and a perpendicular erected at the point 
of tangency K, it will pass through the pitch point P. Now, as the 
gears move in the direction of the arrows, the teeth slide upon each 
other, and the point of contact changes, coming closer and closer to 
point P, then passing through P, and, going on, reaches some point 
as J, which, in the present example, represents the second pair of 
teeth in contact. During all this motion of the teeth, the common 
normal at every point of contact will pass through the pitch point 
P, thus fulfilling the condition of uniform velocity. 

Pressure Line. It will be remembered that the pressure line 
between two surfaces, as illustrated in the discussion of cams, is the 
common normal at the point of contact. Now, a pair of gear teeth 
is like a cam and its follower; and if we wish to find the direction of 
the pressure between them, we simply draw the common normal. 



136 MACHINE DRAWING 

Hence, knowing that with the teeth of proper outline the common 
normal will pass through the pitch point, we merely find the point 
of contact of any pair of teeth and connect it by a straight line to 
the pitch point, thus giving the direction of pressure between the 
teeth at the given position. 

CYCLOIDAL GEARS 

Two kinds of curves fulfill the requirement for gear teeth, that 
the common normal shall pass through the pitch point. These 
are the cycloidal and involute curves. The latter curve, for many 
reasons, has almost entirely displaced the former. The cycloidal 

curve is useful in special cases, 
and is still adhered to by its few 
advocates, as having peculiar 
merit, even for standard work. 
The general and best standard 
practice, however, is unalterably 
committed to the involute sys- 
tem, and experience has shown 
the reasons therefor to be sound 
ones. 

Formation of Cycloidal Curves. 
The student can best approach 
the subject of the design of gear 
teeth through a study of the 

Fig. 113. Methods of Drawing Cycloidal Curves Cycloidal System, the principles 

being capable of clearer illustra- 
tion. Hence this system will be first presented. 

The method of drawing the cycloidal curves by the use of rolling 
circles is illustrated in Fig. 113. The accurate curve, having been 
developed, may be transferred by the tracing-cloth method, as in 
cams, to each individual tooth; or arcs may be found by trial which 
approximate to the true curve; or a templet of stiff paper or card- 
board may be made. 

Design of Epicycloidal Gears. Fig. 114 shows a pair of epi- 
cycloidal gears designed to run together. The centers of the gears 
are at B and A; the pitch circles are shown in dot-and-dash, and 
are in contact at the pitch point P. The circle whose center is C, 




MACHINE DRAWING 



137 



shown dotted, by rolling on the inside of the pitch circle of the gear 
B, generates the hypocycloid PE, which forms the flanks of the teeth 
on gear B; and by rolling on the outside of pitch circle of gear A, 
generates the epicycloid PF, which forms the faces of the teeth on 
gear A. In like manner the circle whose center is D, by rolling on 
the inside of the pitch circle of gear A, generates the hypocycloid 
PG, which forms the flanks of the teeth on A; and by rolling on the 
outside of the pitch circle of B, generates the epicycloid PH, which 
forms the faces of the teeth on B. The circles C and D are called 
the describing circles. If the gear B is the driver and is turning in 




Fig. 114. Construction of Eplcycloidal Gears 

the direction shown by the arrow, the flanks of its teeth act on the 
faces of the teeth on A from the point where they first come in 
contact until the point of contact reaches the pitch point; and from 
the pitch point on until the contact ceases, the faces of the teeth on 
B act on the flanks of the teeth on A. In other words, the hypo- 
cycloidal part of the tooth curve on one gear is generated by the 
same describing circle that generates the epicycloidal part of the 
tooth on the other gear with which it is in contact. This must 
always hold true, in order to have the gears run properly. The arc 
IP of the describing circle C, together with the arc JP of the describ- 
ing circle 2), forms what is called the path of contact; that is, the 
point of contact between the teeth is always somewhere on the 



138 MACHINE DRAWING 

line IP J. If the gear A were the driver, the direction of rotation 
remaining the same, the path of contact would be LPK. 

To design a pair of epicycloidal spur gears, we must have given 
the pitch (either diametral or circular), the diameters of the pitch 
circles, or the number of teeth, and something to determine the size 
of the describing circles. Manufacturers have found by experience 
what are the best ratios of describing circles to pitch circles, and gears 
are designed according to those ratios. It is not well to have the 
diameter of the describing circle greater than | the diameter of the 
pitch circle, and it is better to have it smaller. If a set of gears 
is to be made, any one of which is likely to run with any other one, 
the same size describing circle must be used for the faces and flanks 
of all the gears; and this describing circle is often taken f the diam- 
eter of the smallest gear of the set. Sometimes when two gears 
are not part of an interchangeable set, but are designed to run with 
each other only, the diameter for the describing circle for the flanks 
of each gear is made equal to the radius of that gear; and when 
this is the case, the flanks are radial straight lines; or, as it is usually 
stated, the gears have radial flanks. 

In Fig. 114, the two describing circles are of the same size and 
equal to the radius of the smaller gear, thus giving radial flanks on 
this gear. Let us proceed with the design of this pair of gears, given 
dimensions as follows: Gears to be 4 pitch (that is, as explained 
previously, 4 teeth per inch of pitch diameter) ; gear A to have 12 
teeth; gear B 16 teeth; addendum equal to the diametral pitch; 
clearance equal to J the addendum; describing circles each equal to 
radius of gear A. 

Method of Drawing Gears. The steps in the process of drawing 
the gears are as follows: 

1. Calculate the diameters of the pitch circles. 

2. Draw the center line X Y on the paper; and on this center 
line locate the centers A and B a distance apart equal to \ the sum 
of the two pitch diameters. About these centers draw the pitch 
circles, of diameters as calculated. This will make the pitch circles 
tangent at the pitch point P. 

3. Calculate the addendum and dedendum, adding this 
amount to and subtracting from the radii of the pitch circles. Then 
draw the addendum and dedendum circles with the radii thus found. 



MACHINE DRAWING 139 

4. Draw the root circles with radii equal to the radii of the 
pitch circles minus an amount equal to the dedendum plus the 
clearance. 

5. Draw the describing circles tangent to each other and to 
the pitch circles at the point P. 

6. With the describing circle C rolling on the outside of the 
pitch circle of A, generate the epicycloid PF, continuing it until 
it meets the addendum circle of 'A. With the describing circle D 
rolling on the inside of the pitch circle of A, on the opposite side of 
line of centers from which the circle C rolled, generate the hypocy- 
cloid PG. Since the diameter of D is equal to the radius of the pitch 
circle of A, the hypocycloid PG will be a radial line; and conse- 
quently, after the student has become familiar with this fact, it will 
not be necessary actually to roll the circle to generate such a hypo- 
cycloid. The epicycloid PF and the hypocycloid PG together form 
one side of the tooth of gear A. 

7. Divide the circumference of the pitch circle into as many 
equal parts as the gear has teeth, and through these points draw 
curves like the curve GPF. This may be done by making a templet 
of stiff paper that will just fit the curve GPF, and by means of this 
templet, transferring the curve to the points 1, 2, 3, etc. Next find 
the points, a, b, d, etc., half-way between 1 and 2, 2 and 3, etc., since 
there is to be no backlash, and through these points draw curves 
similar to GPF, but turned so as to curve the other way. Now, by 
filling in with full lines that part of the addendum circle between 
the points F and A", R and S, etc., and filling in the root circle 
between T and V, etc., we have the outline of the teeth on the gear 
A. In practice, instead of making sharp corners at T and V, as 
shown by the dotted lines, fillets are put in with arcs of circles, these 
fillets being made as large as possible and still allowing space so that 
the corner of the teeth on the other gear shall not strike. 

8. Construct the teeth on the gear B in the same way as the 
teeth on A were constructed, the describing circle D generating the 
epicycloid PH by rolling on the outside of the pitch circle of B, and 
the describing circle C generating the hypocycloid PE by rolling on 
the inside of the pitch circle of B. The hypocycloid is not a straight 
line in this case, as the diameter of C is not equal to the radius of the 
pitch circle of B. 



140 



MACHINE DRAWING 



The calculations for the above case are as follows: 4 pitch 
means 4 teeth per inch of diameter; and as there are 16 teeth in B, 

1 A 1 

its diameter will be -^- = 4"; 12 teeth in A will give-j- = 3" diameter. 

The addendum for a standard machine-cut gear is usually made 
equal to the dedendum, and is equal to the reciprocal of the pitch. 




M-"' 



Fig. 115. Layout for Annular Gears 



Hence, to find the addendum and dedendum in the present case, 

take the reciprocal of 4, which is J". 

The clearance, being J the addendum, is equal to J of \ = ^V- 
If the student tries to follow the above description by actually 

drawing these gears, it will be found necessary to draw them to about 

3 times their actual size in order to bring out the points clearly. 

That is to say, the pitch circles should be made 9" and 12"; the 



MACHINE DRAWING 



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addendum and dedendum f"; the clearance ; 



141 
the numbers of 



teeth, of course, remaining 12 and 16. 

ANNULAR GEARS 

An annular gear is a ring with teeth on the inside of it. Fig. 115 
shows such a gear, with center at A, meshing with its pinion. The 




Fig. 116. Construction for Epicycloidal Rack and Pinion 

method of drawing such a pair of gears is similar to that just de- 
scribed for two spur gears. Here the circle C, by rolling on the inside 
of the pitch circle of A, generates the faces of the teeth on A; and the 
circle D, by rolling on the outside of the pitch circle of A, generates 



142 MACHINE DRAWING 

the flanks of the teeth on A. The shape of the teeth of the pinion 
in the figure is found with the same describing circles placed at C" 
and D' to avoid confusing the lines. 

In designing an annular gear and pinion, the diameter of the 
gear must never be so small that the distance from center A to center 
B shall be less than the sum of the radii of the two describing circles. 
If this should be the case, the teeth would interfere with each other. 

RACK AND PINION 

A rack is a gear whose pitch line is a straight line instead of a 
circle. Fig. 116 shows an epicycloidal rack in gear with a 16-tooth 
pinion. The describing circles are of the same size in the figure, 
although they might be of different sizes. The teeth on the pinion 
are drawn as described for Fig. 114, the construction lines for drawing 
them not being shown. The curves which form the faces and flanks 
of the rack are cycloids. The describing circle C, rolling on the 
pitch line of the rack, generates the cycloid PF, which forms the 
flanks of the rack teeth; and the describing circle D, rolling on the 
pitch line of the rack, generates the cycloid PH, which forms the 
faces of the rack teeth. The addendum and root lines are drawn 
parallel to the pitch line, and at a distance from it equal, respectively, 
to the distances A and R of the pinion. The teeth are spaced off on 
the pitch line of the rack by laying off the distances PK, KL, etc., 
equal to the circular pitch of the pinion. 

INVOLUTE GEARS 

Involute Compared with Cycloidal Gears. We have seen in the 
preceding pages how the outlines of cycloidal gear teeth are gener- 
ated by a point in a circle rolling on the pitch line. We have noted 
that the point of contact between the teeth is always somewhere on 
the describing circles, drawn tangent at the pitch point. The 
outlines of involute gear teeth, which are far more common than 
cycloidal teeth, are generated by a somewhat similar process. In 
the case of the involute, however, the describing point is located on 
a straight line, rolling, not on the pitch circle, but on another circle 
inside the pitch line, known as the base circle. The result of rolling 
a straight line, as noted above, is the same as if we stand up on the 
drawing board a small cylinder of diameter equal to the base circle, 
fasten one end of a string to some point in its circumference, and then 



MACHINE DRAWING 



143 



allow the string to unwrap from the cylinder, a pencil point at the 
free end of the string marking on the paper below it the involute 
curve. 

Design of Involute Gears. The method of drawing the involute 
curve is shown in Fig. 117; and it is obvious from this figure that 
the curve can never extend inside the base circle, although it may 
go any distance above it. 

Fig. 118 shows a pair of gears with involute teeth, drawn accord- 
ing to the principles stated below. The circular pitch and diameters 
of pitch circles are calculated in the same way as described for 
cycloidal gears. The centers A and B are chosen, and the pitch 
circles drawn tangent at the pitch point P, as before. In involute 
gears, the point of contact be- 
tween the teeth is always some- 
where on an inclined line, CD, 
passing through the pitch point. 
The angle which this line makes 
with the tangent XY, is called 
the angle of obliquity (equal also 
to PBD). Its size has an im- 
portant bearing on the action of 
gear teeth; and there are special 
conditions which, for the best 
tooth action, would call for widely 
different angles. It is not well, 

however, tO have the angle Of Fi ^ 117 « Method of Drawing Involute Curves 

obliquity of different values, as it would then be impossible for any 
two gears to run together, except those based on the same angle. 
The angle of obliquity which has been quite generally adopted and 
which seems to fulfill the average conditions best, is 15°. In the 
present case, therefore, draw the line CD at an angle of 15° with 
the tangent XY; with A and B as centers, draw circles tangent 
to CD; these circles are called the base circles. The addendum, 
dedendum, and root circles are then drawn at the same relative 
distance from the pitch circles as in the case of cycloidal gears. 
The spacing of the teeth is now accomplished by stepping the dividers, 
set to the circular pitch, around the pitch circle. At any convenient 
points on the base circle, as G and E, generate the involutes in 




144 MACHINE DRAWING 

accordance with the method of Fig. 117, or as explained in Mech- 
anical Drawing, Part II. Then, by the tracing-cloth method, or 
by the use of a templet fitted to this curve, draw in the tooth curves 
at points R, S, T, etc., on the pitch circles. This gives us the work- 
ing part of the teeth, and the remainder of the tooth to the root 
circle consists of a radial line. Fillets are put in at the bottom of 
the teeth, as in the case of cycloidal gears. 

As has been stated above, the point of contact between the teeth 
is always somewhere on the line CD; it is therefore obvious that, 
if the circle struck through the top of the tooth on one gear cuts the 
base circle of the other gear at a point outside of point C, there can 



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be no true contact at the top of the tooth. Instead of there being 
true contact, the top of the tooth will actually dig into the lower 
portion of the tooth of the other gear. This is known as inter- 
ference, and is overcome by slightly rounding off the top of the tooth 
down to the circle through point C, so that it will clear. Since the 
path of the point of contact is along the line CD, this line also repre- 
sents the common normal to any pair of teeth in contact, and there- 
fore is the line of pressure between the teeth. The obliquity of this 
line of pressure to the line of centers AB causes a thrust between 
these centers, tending to force the gears apart; and this has been 



MACHINE DRAWING 145 

considered an objection to the use of involute gears. With the 
standard 15° involute, however, experience has shown that this 
thrust is ordinarily of small importance. A similar thrust exists in 
cycloidal gears, but is constantly changing in value, being a maxi- 
mum at the beginning and end of contact of a pair of teeth, and 
zero when the pair of teeth are in contact at the pitch point. It 
will be noted that the involute tooth is of simpler outline than the 
cycloidal, being a single curve instead of a reverse curve. If the 
exact distance between the centers A and B of a pair of involute 
gears be not maintained, owing to wear or to some other cause, the 
gears will still continue to run perfectly together; whereas in the 
case of cycloidal gears the action is seriously impaired by such a 

condition. 

BEVEL GEARS 

Bevel gears are used to connect shafts whose axes intersect. 
The angle between the shafts is not necessarily a right angle, but 
this is the most common angle used. Fig. 119 shows a pair of bevel 
gears connecting two shafts whose axes intersect at a right angle. 

The cones OP A and OPB are called pitch cones; the cones CPB 
and DP A, normal cones, and it is on these normal cones that the 
outlines of the teeth are laid out; BP and AP are the pitch diameters 
of the gears, and are found from the pitch and number of teeth just 
as the pitch diameters of spur gears are found. 

Design of Bevel Gears. To draw such a pair of gears, we must 
have given the angle between the shafts, the pitch and number of 
teeth in each gear, and the face of the tooth PE. The outlines of 
the teeth may be either involute or cycloidal; the addendum, deden- 
dum, and clearance are determined by the same empirical rules as 
were applied to the other gears which have been discussed. 

Referring to Fig. 119, the gears shown are 2-pitch, 16 and 20 
teeth, respectively, with face PE equal to 2 inches. 

According to previous understanding, the addendum or the 
dedendum for a standard tooth is the reciprocal of the diametral 
pitch — or, in this case, f ". Making the clearance J of the addendum, 
would give f of |" = tV" • The teeth are of the involute form, with an 
angle of obliquity of 15°. Choosing point 0, draw the lines 0C and 
0D, making an angle of 90° with each other; calculate the pitch 
diameters of the gears; lay off on 0C the distance OH, equal to § 



146 



MACHINE DRAWING 



the pitch diameter of the smaller gear; and through H draw a line 
perpendicular to OC. In like manner lay off on OB the distance 
OJ, equal to J the pitch diameter of the larger gear; through J draw 
a line perpendicular to OB, meeting the perpendicular which is 



'--PITCH C/RCLE 




Fig. 119. Construction Diagram for Pair of Bevel Gears 

drawn through H at P; and make HB equal to HP, and J A equal 
to J P. From A, P, and B, draw lines to 0, producing the pitch 
cones; through P draw CD perpendicular to OP, meeting OC and 
OB in C and B, respectively. Join CB and BA, and we have the 
normal cones. Through C, P, and B, draw perpendiculars. Draw 



MACHINE DRAWING 



147 



LMK parallel to CPD at any convenient distance. Draw arcs of 
circles tangent at the point M. These arcs are now to be treated 
as pitch circles on which to design the tooth curves, in exactly 
similar fashion to the method already outlined for spur gears. 

Through point M draw the line of obliquity SR, and draw the 
base circles tangent to this line. With the addendum chosen as 
above, equal to ¥ , it will be found that the addendum circle of the 
larger gear will cut the line of ^obliquity beyond the point R, where 
SR is tangent to the base circle of the pinion. This means that true 
contact cannot occur at the top of the gear tooth, so the tooth 
should be slightly rounded off, to prevent interference with the 
flank of the pinion. The limit of this rounding-off of the point of 




Fig. 120. Skeleton Diagram for Bevel Gears not at Right Angles 

the tooth is determined by striking a circle with center L through 
the point R, as it is obvious that below this point on the tooth of 
the gear there will be true involute contact. The root circles are 
drawn by setting off the clearance, as in the preceding cases. One 
tooth on each gear is drawn on the development of the pitch circle, 
and the completion of the drawing of the teeth in the several views 
of the gears is merely a problem in projection. 

With L as a center, draw a series of arcs (shown dotted) cutting 
the tooth which was drawn on the pitch circle, and the line LMK, 
at 2, 3, 4, etc.; from 2, 3, 4, etc., draw lines perpendicular to CD, 
cutting CD at 5, 6, 7, etc.; from these points draw lines to 0; along 
P0 lay off PE; through E draw a line perpendicular to PO, cutting 



148 MACHINE DRAWING 

50, 60, etc.; and from the points of intersection draw other lines 
parallel to PB. With center f , taken at any convenient place on 
CO prolonged, and with radii equal in turn to a5, b6, etc., draw 
circles as shown. On the circle which is drawn with HP as a radius 
(marked "pitch circle"), space off the circular pitch; and on each of 
•the circles in turn, lay off the teeth of the same width as they are 
on the corresponding circles drawn through 1, 2,3, 4> etc. The rest 
of the construction can be understood by a careful study of the figure. 
The other gear is drawn in the same way. 

Intersecting Angles Other than 90°. The drawing of the teeth for 
bevel gears whose shafts intersect at another angle than a right angle, is 
accomplished by following out the same principles as noted in the case 
at hand. The skeleton outline of such a pair of gears is shown in Fig. 
120, the angle between the axes being 60°. These gears are 2-pitch, 
16 and 20 teeth, respectively, the same as in the previous case; and 
their construction affords an interesting comparison therewith. 

General Manufacturing Practice. To draw the teeth on a pair 
of bevel gears as described in Fig. 119, is a tedious process and 
requires considerable patience and drafting skill. It is really little 
more than an exercise in advanced projection drawing, but, as such, 
is valuable to the student. It must not be thought, however, that 
to detail a pair of bevel gears for manufacture, such a drawing is 
necessary. Usually, standard proportions of teeth are specified, and 
the detail of the gears is comparatively simple. An illustration of 
a pair of bevel gears of standard proportions of teeth, detailed ready 
for the workman's use, is shown in Fig. 39, Machine Drawing, Part 
I, and it is seldom necessary to show more. 

General Remarks on Gear Teeth. The foregoing study of the 
outlines of gear teeth is given in brief and elementary form. The 
student cannot hope to gain a familiar comprehension of the action 
going on between the teeth of gears, without going more deeply into 
the subject than is possible in these pages. The action of gear teeth 
is one of the most complicated subjects to investigate and under- 
stand, as with each new condition of number and type of teeth, new 
points of action are developed. 

A good practical article on gear teeth is "A Treatise on Gear 
Wheels" by George B. Grant; and the student is referred to this book 
for a further study of the subject. 



MACHINE DRAWING 149 

There are many special points to be observed in designing the 
outlines of gear teeth, in order to insure the best operation of the 
gears. These points cannot be well explained without the actual 
undertaking of the design of the teeth. If the student wishes to 
familiarize himself with tooth action, he cannot do better than to 
choose a variety of cases, and lay out each one, studying the several 
points as they come up. 

It should be remembered that the action of a small pinion, 
meshing into a large gear is considerably different from that of two 
large gears meshing into each other. With certain relative numbers 
of teeth of gear and pinion, as many as three pair of teeth may be in 
contact at all times; while, in certain other combinations, but two 
are in contact at all times, and in certain others only one. Changes 
in the tooth dimensions, diameters of describing circles, angles of 
obliquity, etc., alter all these conditions, so that there is an endless 
variety of combinations, each of which presents some new feature 
only to be understood by actual layout of the particular case. 

In gear-tooth work, the student will often find it an advantage 
to make the layouts to double the actual size, and sometimes larger. 
A fine, hard pencil must be used, and extreme accuracy in deter- 
mining the points must be adhered to. The layout of gear teeth is 
one of the severest tests of the draftsman's ability in line work. 

PLATES 

Plates V to X, inclusive, are to be drawn by the student for 
practice in applying the principles of screws, springs, cams, belts, 
and gears. These plates are to be made the same size as those of the 
preceding Instruction Papers of the course; viz, 11" by 15", outside, 
with a margin of J", making the clear space for the drawing 10" by 
14". 

PLATE V 

Fig. 1. Make a theoretical drawing of a right-hand, single, 
sharp V thread screw, 4" in diameter, 6" long, 1" pitch. Construct 
the true helix as shown in Fig. 62 of the Instruction Paper. Show 
dotted construction lines for one complete turn of the helix. 

Fig. 2. Make a conventional representation of a single right- 
hand, square-thread screw, 2" in diameter, 3J" long, J" pitch (2 
threads per inch). 



150 MACHINE DRAWING 

Fig. 3. Make a conventional representation of a single, right- 
hand, U. S. standard V thread screw, 2" in diameter, 3§" long, 4J 
threads per inch. Use form shown in Fig. 74. 

Fig. 4- Make a conventional representation of a single, right- 
hand, sharp V thread screw, 1" in diameter, 3J" long, 8 threads per 
inch. Use form shown in Fig. 73. 

Fig. 5. Same as preceding figure except make left-hand, and 
double thread. 

Fig. 6. Draw a right-hand helical spring, T \ -inch round wire, 
inside diameter of spring If", length 3|", pitch f", using form 
shown in Fig. 58. 

All the figures on this plate are to be made and inked in on the 
drawing paper. . 

PLATE VI 

Fig. 1. Draw a plate cam, the top turning to the right, to raise 
a slide (having a roll at its lower end) 1J" with harmonic motion, 
while the cam turns through 135°, then to allow a fall with uniform 
motion while the cam turns through 180°, and rest for the remaining 
45°. Make the center line of motion of the slide pass through the 
axis of the cam, the roll 1" in diameter, and at its lowest position 
\y above the axis of the cam. Show one view only, and do not 
show the shaft or hub of the cam, these being merely explanatory on 
the plate as shown. Use a hard pencil, with a fine point, and show 
pressure lines. 

Fig. 2. Draw a plate cam, the top turning to the left, to raise a 
roll, similar to that of the preceding figure, 1§" with uniform motion, 
while the cam turns through 150°, then to rest for 30°, then to fall for 
the remaining 180° with a uniformly accelerated and retarded 
motion. Make the center line of motion 1" to the right of the axis 
of the cam, and at its lowest position the center of the roll 1|" (meas- 
ured radially) from the center of the cam. Show pressure lines. 

As inking will impair the accuracy of both of the figures on this 
plate, it should be handed in just as the pencil work leaves it. Special 
care must be taken to have the lines fine, sharp, accurate, and clear. 
Accuracy is of first importance in this case, and though the plate 
should be cleaned up as much as possible without destroying the con- 
struction lines, yet it cannot be expected that the plate will be as clean 



- MACHINE DRAWING 151 

when finished as though it were inked, thus giving opportunity to 
rub over the whole drawing. 

PLATE VII 

This shows plan and one elevation of two pulleys located on two 
shafts at right angles to each other. Draw these two views and 
another elevation, showing the belt on the pulleys in all three views, 
and place arrows to show the direction of motion of the pulleys in 
order that the belt may stay on. The dimensions are given in feet 
and inches, but the drawing cannot be made full size. As stated in 
the title, the scale may be 1" per foot, that is, the distance between 
the shafts being 8', it is made on the drawing 8". Other dimensions 
are to be reduced in the same proportion, or to one-twelfth size. 
This plate should be inked in on the drawing paper. 

PLATE VIII 

Fig. 1. With center 3" from the extreme left of the sheet, and 
on a horizontal line through its middle, strike the arc of a pitch 
circle with 6" radius. Take describing circles of 4" diameter, and roll 
them upon both sides of this pitch circle, producing at least three 
epicycloidal teeth, diametral pitch 1J, addendum §", dedendum § ", 
clearance J", thickness of tooth equal to one-half the circular pitch. 
Note that the diametral pitch, 1J as given, is not "inches", but num- 
ber of teeth per inch of diameter of pitch circle. In order to lay out 
the teeth, the circular pitch must be calculated as explained in the 
Instruction Paper. 

Fig. 2. With center 5|" from the extreme right of the sheet, 
and on the same horizontal line as before, strike the arc of a pitch 
circle with 6" radius. Take angle of obliquity equal to 15°, and 
draw the base circle for involute teeth. Draw at least three full 
involute teeth, diametral pitch 1J, addendum §", dedendum §", 
clearance |", thickness of tooth equal to one-half the circular pitch. 
As before, the circular pitch must be calculated, and when the teeth 
are finished it should be noted how different is the shape of the 
involute tooth from the epicycloidal, yet both are correct working 
teeth for the same diameter of pitch circle. 

Both figures of this plate should be handed in just as the pencil 
work leaves it, for the same reasons as for Plate VI. 



152 MACHINE DRAWING 

PLATE IX 

Draw a horizontal line through the middle of the sheet, and, 
choosing a center 1" from the left-hand side of the sheet for the 
pinion, draw an 18-tooth pinion meshing with a 30-tooth gear of the 
involute, spur-gear type. Make teeth 2 diametral pitch, angle of 
obliquity 20°, addendum J", dedendum J", clearance T V, thickness 
of tooth one-half the circular pitch. Draw as many teeth as there 
is room for across the plate, show the length of the path of contact, 
and state the greatest number of teeth which can be in action at any 
one time. 

This plate should be inked in with as fine lines as possible, in 
order not to greatly impair the accuracy of the work. 

PLATE X 

Draw a horizontal line 5f " from the bottom of the sheet and a 
vertical line 4" from the left-hand side as axes for a 27-tooth bevel 
gear and a 16-tooth pinion respectively. Make the teeth 4 diametral 
pitch, addendum J", dedendum \", clearance 3V, length of face 1|". 
Make an outline like Fig. 120, indicating the pitch diameters, pitch 
cones, and normal cones. 

This plate should be inked in, fine lines being used for the con- 
struction lines, and heavy ones for the body of the gears, which may 
be made any proportions to suit the student's conception of what they 
should be. This may be treated as a case for development of the 
student's mechanical judgment and sense of proportion, based, of 
course, on the exact skeleton outline made from the data as given. 

EXAMINATION PLATES 

Drawing Plates V to X, inclusive, constitute the Examination for this 
Instruction Paper. The student should draw these plates and send them to 
the School for correction and criticism. 

Reproduced plates of Nos. VIII, IX, and X, are not sent to the student; 
he should work out the problems for himself, following the directions given. 

The date, student's name and address, and the plate number, should be 
lettered on each plate in inclined Gothic capitals. 



MACHINE DRAWING 



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MACHINE DRAWING 

PART III A— MECHANICAL 



WORKING SHOP DRAWINGS 

In Mechanical Drawing, Parts I to III, inclusive, the funda- 
mental principles were explained and illustrated. In Machine 
Drawing, Parts I and II, the production of working drawings has 
also been discussed to some extent, and the usual characters and 
symbols explained and applied. The elementary work already out- 
lined has been treated chiefly from the standpoint of correctness of 
line representation considered by itself, without a detailed study of 
the use to which the drawings so produced are to be applied. 

Evidently this is the proper method, for the student should 
gain a thorough understanding of the principles which underlie line 
representation before attempting to apply them to any extended 
practical use. In all of this preceding work it was intended that 
the theoretical principles should overshadow any incidental refer- 
ences made to practical application, however true and pertinent 
the latter may have been for purposes of illustration. Hence, before 
taking up any advanced work, the student should fully realize the 
importance, in fact, the absolute necessity, of thoroughly under- 
standing the fundamental principles which have been outlined in 
the preceding books. 

At this point the student must realize that a lack of proper 
elementary and fundamental training will make him "go lame" at 
every point of his course, and probably prevent the attainment of 
proficiency which otherwise would naturally and almost instinc- 
tively come with advanced study. It is thorough and ready knowl- 
edge, always at his fingers' ends, of all the principles of Mechanical 
Drawing, which makes the expert draftsman. 

Plan and Scope of Advanced Work. Utility the Guide. It is 
now intended to throw an entirely different light on the matter, and 



158 MACHINE DRAWING 

view the subject of Machine Drawing from a purely practical stand- 
point, that of utility. It is assumed that the student understands 
and can use the principles which have been previously discussed. 

If in a working shop drawing we choose to modify any of these 
theoretical principles, it will be because of increased value in the 
utility of the drawing. For example, we may desire to omit some 
portions of an elevation or plan or side view of a complicated cast- 
ing, because certain details will thus be more clearly brought out. 
We may make a "zigzag" section to show construction which, by 
absolute fidelity to theoretical principle, would be confused, or hid- 
den in a maze of dotted lines. We may find it convenient to place 
in some unoccupied corner of a drawing a layout which could not 
be in the least justified by any rule of projection. A multitude of 
transgressions like these occur on good drawings, and they are 
certainly justifiable from the standpoint of utility, which is the true 
ultimate end sought for in a practical shop drawing. 

These variations from the theoretical are not strictly conven- 
tionalities, because they are not classified or established, so far as 
we know, but are the spontaneous outgrowth, as the occasion de- 
mands, of the draftsman's purpose to make his drawing one of 
greatest utility. He can, however, safely transgress a principle only 
when he thoroughly knows the principle; otherwise a blind deviation 
from the theoretical path will inevitably lead to difficulty. 

^.11 of the above is intended to impress the student with the 
idea that theoretical principles are his best, in fact, his only tools 
to work with; but they are not "self-hardening," like "mushet" 
steel; they are like the finest grade of tool steel, which must be 
tempered and ground and used with the best judgment of the oper- 
ator, to secure the most satisfactory results. 

Student Drawings. A student's early drawings are usually 
unsatisfactory, even to himself. Somehow they do not look like 
those seen in shops, and as a rule he is unable to see why this is 
so. Of course the difference is to some extent due to the experi- 
ence of the professional draftsman. However, the superior results 
of the latter' s work are attained largely through his systematic 
and workmanlike habits of execution. It should encourage the 
student in his early attempts to know that these essentials to the 
infusion of life and shop spirit into a drawing can be analyzed, out- 



MACHINE DRAWING 159 

lined, and grasped at the outset by earnest, intelligent effort, and 
really good workmanlike results obtained. To discuss and, if possi- 
ble, to impart these essentials of a working shop drawing to the 
student, is the purpose of the present book. 

Essential Requirements. The two chief essentials of a shop 
drawing, under which general heads a multitude of detail require- 
ments can be summed up, are : 

(1) Absolutely complete and definite instructions from- de- 
signer to workman. 

(2) Least possible cost in dollars and cents of production of 
the drawing measured by the draftsman's time. 

It makes no difference how much we may attempt to disguise 
these two elements, the fact will still be apparent that "complete 
instructions furnished for the least money" is what the manufac- 
turing shop is after, and what will be assumed as a basis for judg- 
ment as to highest commercial utility. 

Completeness of Drawings. As to the first point, that of com- 
pleteness and definiteness of instruction, there must be no question 
of degree. If the information which the drawing furnishes is posi- 
tive and complete, the drawing is good. If doubt arises in the 
workman's mind as to what the designer intended by a certain line 
or dimension, or if the dimension be omitted, the drawing is bad. 
There is no middle ground. The instructions are either present or 
absent, and the drawing good or bad accordingly. 

The workman of today is not permitted to assume dimensions 
or shape. It is his business to execute the draftsman's orders; it 
is, however, often his privilege to choose his own way of doing it, 
but further than this modern practice does not allow him to go. He 
is held as rigidly to the orders specified by the drawing as the loco- 
motive engineer is held to his bit of tissue telegraphic order to pro- 
ceed, without which he dare not enter the next block. The drawing 
is supreme; it is official; it must be plain, direct, and all-sufficient. 
It is the draftsman's business to make it thus, and he is not a drafts- 
man until he does. 

This idea uf positiveness must be thoroughly absorbed by the 
student. Positive action must be a habit which controls his every 
move, which marks every dimension he prints, which directs every 
line he draws. Every line must mean something, must have a 



160 MACHINE DRAWING 

definite reason for existence, must be necessary to illustrate the 
idea which he wishes to convey to the workman, and every line 
must be a definite measurable distance from every other line, so 
that its location is fixed beyond a doubt. Lines which mean nothing, 
and cannot be measured, have no place on the drawing; they only 
confuse it. 

A good picture of a machine could scarcely be called to the 
same service as a good drawing of it. The picture might give us 
an excellent idea of the machine, but for the purpose of the actual 
construction the picture is useless, while the drawing is of positive 
value. This value exists simply because of, and in proportion to, 
the completeness of detail which it shows. Hence in making a shop 
drawing the picture idea is entirely subordinate to the idea of utility, 
the latter, in fact, being the measure of its value. 

There are certain classes of drawings — of which the Patent 
Office drawing is a good example — in the making of which the 
picture idea is predominant. Here the purpose is to illustrate 
mechanisms, not construct them; hence the function of the drawing 
is in no wise that of the working shop drawing, and as such does not 
fall within our discussion. 

Cost of Producing Drawings. The second general element 
involved in producing shop drawings is their cost, as measured by 
the draftsman's time. It is somewhat subordinate to the first 
element, for the drawing must be a good one, judged by an absolute 
standard, whatever the time or cost necessary to produce it. Cost, 
however, is an important item, and cannot well be overlooked. It 
is inevitable that in any enterprise economy will ultimately be 
sought, whatever extravagance an imperative original demand may 
have permitted. This is as true in the production of drawings as 
in the case of manufactured articles of trade. Drafting-room labor 
is a relatively high-priced service, and the salary list easily assumes 
considerable proportions, so that wasteful excesses count up rapidly. 
One of the qualifications of proficiency invariably required for this 
department of shop organization is rapidity of execution. This 
is not as dependent upon personal traits as at first might be supposed. 
A man may so husband his time and direct his efforts that he will 
easily distance his neighbor of more rapid motion. The latter may 
have less ability to make his energies count, and lack of judgment 



MACHINE DRAWING 161 

as to when just enough, and no more than enough, energy has been 
expended on his drawings. From the standpoint of utility, the 
function of a drawing is fulfilled when it has reached the stage that 
it completely instructs; more time spent in elaboration is wasted, 
and is an unnecessary and therefore extravagant expenditure. The 
student must fully realize this. In his earnestness to produce fin- 
ished and complete work he must constantly strive to accomplish 
results in the least possible time. This does not mean careless 
haste; far from it. A complete shop drawing cannot be made by 
short cuts, but through a systematic building of line on line, dimen- 
sion on dimension. This is in sharp contrast to a haphazard habit 
of developing a drawing, first a line here and then a figure there, 
with no definite purpose in mind, and no hint as to when the drawing 
is actually completed. 

The one method constitutes the efficient draftsman who works 
easily, receives a high salary, and is worth it, because he wastes no 
time in unnecessary labor. The other marks his unfortunate 
brother, plodding laboriously far behind, receiving a small pittance 
per hour, and worth less, because he does uncalled-for labor, and 
loses his definiteness of purpose in a maze of unexplainable lines and 
figures. 

A working shop draiving, commercially considered, may well 
be defined as being "Complete instruction from designer to workman 
issued at minimum expense." 

This definition should be memorized by the student, and con- 
stantly kept in mind while making a drawing. The preceding 
pages should be re-read with this in view until the full spirit is 
appreciated. 

The maxim as given above, if faithfully adhered to without 
modification, answers nearly every question that can be raised as 
to the excellence of a drawing. It can be used as a standard of 
judgment, whatever system of lines or symbols may be in vogue. 
It permits a draftsman to adjust himself to the rules of any shop 
or drawing room, and yet produce a good drawing and satisfy his 
employer. 

A drawing which is cheaply produced yet at the same time 
does perfectly that for which it was made, viz, conveys complete 
instruction, is beyond commercial criticism. 



162 MACHINE DRAWING 

Method of Procedure. As the general objects to be attained 
in a working shop drawing have now been presented, it is necessary 
to indicate in detail how the work may be properly accomplished. 
In order to do this, it is proposed to produce systematically a full 
set of working drawings of a familiar and comparatively simple 
machine. The methods used will be those of a designing detail 
draftsman, producing commercial work fit for shop use. In the 
progress of the work, from its beginning in the rough, though accur- 
ate, pencil layout, to the completion of the tracings and the order 
sheets, the same bold style, clearness, directness, and businesslike 
spirit which the shop atmosphere and surroundings would naturally 
supply will be emphasized, and so far as possible imparted to the 
student. It is expected that the student will follow the text closely 
and study the plates carefully, endeavoring to familiarize himself 
with every detail illustrated. The more closely he is able to apply 
himself in this respect the better will he be able to partake of the 
life and spirit which is intended to be conveyed, and without which 
the true character of the work can be but poorly developed. 

Incidentally, several purposes will be fulfilled by this treatment. 

Practice in Reading Draivings. Ability to read drawings 
quickly and intelligently is almost as important as making them, 
and it is expected that the study of the plates, with a view to thor- 
oughly understanding every line, will develop proficiency in the art 
of reading drawings. 

Discussion of Tools and Machine Parts. The discussion in the 
text of not only the form of the machine parts themselves, but also 
the tools and shop processes to produce them, affords considerable 
insight into the influences affecting good machine design. Without 
introducing any mathematical analysis or investigation, which is 
beyond the province of this book, much practical consideration as 
to the restrictions imposed by existing shop methods upon theoretical 
construction will be suggested, and the student encouraged to use 
his judgment thereon. 

Imitation of Pencil Sketches. In the preliminary layouts 
the actual "sketchy" appearance of the pencil drawing will be 
imitated as far as possible, so that the student himself may imitate 
and catch the bold dash, yet fine accuracy, of the linework, which 
is characteristic of the expert draftsman. 



MACHINE DRAWING 163 

Making of Complete Draicings. The completeness of a set of 
drawings is as important a lesson as the completeness of each draw- 
ing itself. In this is involved the proper arrangement and classi- 
fication of details, the foundation layout, and the system of order 
sheets for getting work into and through the shops. This is a 
feature which very strongly affects some of the finishing touches to 
a drawing, for it is so easy to omit a "few last things" and turn in 
an uncompleted sheet. Every draftsman knows how many little 
tilings come up toward the close of a job involving complete draw- 
ings of a machine, and how strong the tendency is to omit them, 
and relieve himself of somewhat tedious details. The result is 
irritation and delay when the drawings get into the shop, and they 
return to the drawing room to be fixed up at a time probably incon- 
venient for all parties concerned. A good draftsman will turn in a 
complete set of complete drawings. It is highly important that the 
student grasp this idea, and study his work accordingly. 

DUPLEX PUMP PLATES 

Reasons for Choice of Pump Specifications. The typical set of 
plates chosen for this book in fulfillment of the above purposes, 
takes up the study of a simple, duplex steam pump. This particular 
type of machine represents the simplest and most elementary form 
of the steam engine in modern use in respect to valve gear and con- 
trolling devices. It is not an economical machine, yet its principles 
lie at the foundation of the economical high-speed engine, the latter 
being produced through a modification of the uneconomical valve 
gear such as is found on a pump of the type chosen, rather than 
through any radical change of construction as to the body of the 
machine. Hence the study of a steam pump may well precede that 
of higher forms of the steam engine. It is hoped that the study w T ill 
so interest the student that he will be led to further investigation 
and development not only of the steam engine itself, but of that 
highly important division of modern engineering — pumping 
machinery. 

Thus we note another point of advantage in the study as out- 
lined. The power end of the machine introduces us to the steam 
engine; the load end is the beginning of the engineering of pump- 
ing machinery. 



164 



MACHINE DRAWING 




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MACHINE DRAWING 165 

Rating of Pump. A steam pump is rated by the bore of its 
cylinders and length of stroke, all being given in inches. A 
"16X8JX12 pump" means that the steam cylinder is 16 inches 
in diameter, the water plunger 8J inches in diameter, and the nom- 
inal length of stroke 12 inches. These sizes are always given in 
the same order, beginning with the diameter of the smallest cylinder 
(in case there is more than one), then the diameter of water plunger, 
the common stroke of both being placed last. This expresses to 
the mechanic the rating of the pump in the clearest style and briefest 
language. 

The pump illustrated here is designed for standard service, 
operating under a steam pressure not to exceed 100 pounds per 
square inch, water pressure not to exceed 150 pounds per square 
inch, and the rated capacity based on an average piston speed of 100 
feet per minute being about 550 gallons. This requires that each 
side of the pump shall handle 275 gallons and, being double acting, 
shall make 100 reversals or 50 double strokes per minute. 

PLATE A. STEAM END LAYOUT 

This plate illustrates, as nearly as reproduction can accomplish, 
the pencil layout of the steam end. It is the first work of the design- 
ing draftsman. The drawing as shown is exactly the type of layout 
which he would turn over to a detail draftsman, whose duty it would 
be to work up detail shop drawings therefrom. 

Characteristics of a Layout. The character of this drawing 
should be carefully studied. Remember that it is a layout, nothir.g 
more; also bear in mind that it is an exact, measurable working 
sketch. Attention is called to the sharpness of the lines, especially 
to the clean-cut intersections. Note the boldness, dash, and business- 
like style, the freehand cross-section lines roughly put in. There is 
no hesitation or worry as to where the end of a line shall be, or 
whether it crosses other lines which it theoretically should not. 
The intersections are allowed to indicate the termination of lines, 
and the rough section lines pick out the parts and separate them 
clearly to the eye. There is, in this layout, the spirit of confident, 
definite, and rapid action, with no thought for absolute finish in 
linework, but with every thought for absolute results as to measur- 
able dimensions. 



166 MACHINE DRAWING 

Relations of Different Drawings. The data for the production 
of Plate A by the student are rather more complete than he would 
usually find in practice. Plates B, C, and D show many details 
fully. 

The steam cylinder and head, however, as shown in Plate B, 
are not dimensioned, and the student's problem is to produce this 
plate complete, with finish marks, dimensions, and necessary data 
for a working drawing. In order to do this it is first necessary 
to work up Plate A with exactness, in pencil, and see that all parts 
go together properly. Then the detail of cylinder and head may 
be made separately by measurement of the layout drawing, and 
Plate B produced. 

For this work the ordinary brown detail paper is very satis- 
factory. A hard lead pencil is necessary, as hard as 6H, and the 
point must be kept well sharpened. 

Rules of Action. There are two general rules of action in pro- 
ducing a drawing which give the answer to the question which fre- 
quently confronts the beginner: "What is to be done first?" or "What 
is to be done next?" These rules are : (1) Draw everything that is 
positively known; and (2) work from the inside to the outside. 

Every problem has some positive data, assumed or calculated, 
to start with. The first thing to do in every case is to get this 
data represented by lines on the paper. An expert designer has 
been heard to say that until he had spoiled the blankness of his 
sheet of paper by some lines, he could not design. There is some- 
thing in this; and almost invariably the first line to draw is a hori- 
zontal center line somewhere near the middle of the sheet; draw 
it! Draw it at once without hesitation, and the layout is begun. 
We now have something about which to build. 

Development of Layout — In this case the designer would first 
calculate the size of the piston rod, and determine the fastening to 
the piston. He would then draw the rod and build a hub around it. 
He would next calculate the width or thickness of piston and size of 
packing rings, and draw the two vertical lines 5 inches apart, to indi- 
cate the piston faces. These lines would be limited by the cylinder 
bore, which he knows to be 16 inches; hence horizontal lines 16 
inches apart, parallel to and symmetrical with the center line, are 
the next to be drawn. Short vertical lines indicate the location of 



MACHINE DRAWING 167 

the packing rings. As the nominal travel of the piston is to be 12 
inches, the location of the piston and rings can be shown on both 
sides of the central vertical line at the limits of travel. A clearance 
must exist between the heads and the piston (in this case \ inch is 
allowed), hence the lines of the heads can be drawn, and the general 
inside outline of the cylinder barrel is complete. 

This is all in direct' application of the foregoing rules, and is 
so simple, natural, and direct that it hardly requires such explicit 
statement. We have simply taken such data as we had and put 
it on paper, placing it where it can be seen from all sides, and where 
the mind is relieved of the labor of carrying it. 

If the student will only appreciate this one rule and draw all 
he knows about the problem, he is well on his way to its solution. 
Draw everything you know, and tvork for ivhat you don't know is what 
these two rules say, and the first question to arise should be: "Have 
I drawn everything that is known about the problem?" before he 
asks himself or any one else: "What shall I do next?" 

Dimensions in Even Figures. One other rule might be added 
to these two: Keep dimensions in even figures, if possible. This 
means that small fractions should be avoided. It is just as easy to 
bear this point in mind, and save the workman much annoyance 
and chance of error, as it is to disregard this matter. Even figures 
constitute one of the trade-marks of an expert draftsman. Of course 
a few small fractions, and sometimes decimals, will be necessary. 
Remember, however, that fractions must in every case be according 
to the common scale; that is, in sixteenths, thirty-seconds, sixty- 
fourths, etc. ; never in thirds, fifths, sevenths, or such as do not occur 
on the common machinist's scale. 

A systematic, definite mode of treatment on these lines must 
become a habit, so that all problems, however complicated, can be 
approached with confidence in the same way. It is the drawing of 
one line which makes clear the drawing of the next and subsequent 
lines; and the most serious obstacle which the student is likely to set 
for himself is trying to see the whole problem through from the 
beginning. Even an expert cannot do this, but allows the layout to 
develop results as he proceeds. 

Cylinder Details. The details of the piston and rod being given 
in Plate C, the foregoing work is very easy for the student. The 



168 



MACHINE DRAWING 



thickness of the barrel and heads being determined (J inch in this 
case), the exterior outline may be partially drawn. The fixed head 
at the yoke end must be thicker than this, in order to receive the 
yoke and stuffing-box bolts without breaking through. The recesses 
or counterbores at either end of the cylinder should be so located 
that the packing rings run over the edge a little at the end of the 
stroke, thus preventing the wearing of a shoulder by the piston 
stopping in the same place every time. The counterbore should 
be deep enough to allow reboring the cylinder without the counter- 
bore being touched by the tool. In this way the counterbore is 
retained to center the cylinder at its original location. 

Port Details. The size of steam ports having been calculated, 
they may be drawn in, the turns being made easy and as direct as 
possible. The height to valve 
seat must be kept at the lowest 
limit .consistent with sufficient 
metal between and outside of the 
ports. As the detail of the ports 
might be somewhat troublesome, 
it is shown in an enlarged sketch 
for the student's benefit, Fig. 
121. Chipping or filing strips f 
inch high are left on the port 
edges, which must be true, in 
order to finish them up easily. 

The three inner ports are for exhaust, the outer ones for admis- 
sion of steam. This five-ported cylinder is peculiar to the direct 
acting steam pump, it being a device to effect the cushioning of the 
piston at the end of the stroke, thus preventing the piston from 
striking the heads. This is necessary, since no positive limit of 
motion exists, as is the case in machines with crank and connecting 
rod. 

When the edge of the piston has passed the outer edge of the 
exhaust port, as shown in Fig. 121, the steam, which has been ex- 
hausting through port A, is confined in space B and port C, and, 
being compressed by the piston, acts like a spring to retard its 
motion. If the point P is properly determined for a given speed, 
the piston will always compress the steam just enough to cause it 




Fig. 121. Enlarged Details of Steam Port 



MACHINE DRAWING 169 

to stop at the end of the nominal stroke; in this case, J inch from 
the head. It is evident, however, that at different speeds the piston 
will have more or less power to compress the steam, and will not 
stop at the point desired. This causes the trouble of "short stroke," 
and consequent inability to make the pump work to its full capacity. 
Now if we connect ports A and C by a small opening shown dotted 
at D, and control this opening by a plug valve operated by hand 
from the outside, we can let a little steam leak by into port A, thus 
reducing the cushion and allowing full stroke. 

In order to avoid complicating the drawing, no cushion valves 
are shown or required to be put on by the student. They are not 
customary in small pumps, but might advantageously be put on the 
present illustration. 

The valve seat must be a scraped surface, while the chest face 
need not be; hence the latter is finished J inch lower. This also 
gives a ledge against which the steam chest fits, thus securing posi- 
tive location. 

Cylinder Heads and Steam Chest. The bolting of the heads 
and the steam chest should allow a width of packing inside of the 
bolts of | to f inch, otherwise there is danger of the steam blowing 
out the packing and causing leakage around the bolts. The bolts 
do not fill the holes, the latter being drilled large, from ye to § inch. 
The spacing, if wider than 5 or 6 inches, is likely to permit springing 
of the flanges between the bolts, and consequent leakage. Bolts 
less than f-inch diameter are not desirable, as they can be easily 
twisted off with an ordinary wrench. In this case the cylinder head 
takes | -inch bolts, the yoke, stuffing-box, and gland, f-inch. 

The flanges of heads and cylinders are usually from 25 per cent 
to 50 per cent thicker than the body of the casting. 

Drips, J-inch pipe tap, to be fitted with cocks, are necessary at 
both ends of the cylinder to readily drain the cylinder of water. 

Molding Steam Cylinder. The design is often influenced by 
the way in which the piece is to be cast. It often takes but a slight 
change of design to save many dollars in pattern making and foun- 
dry work. Hence the habit should be formed of always judging 
the design of a piece from the foundry standpoint. In this case it 
is evident that the ports and cylinder bore must be cored out, and 
the most obvious position of molding is to lay the cylinder on its 



170 MACHINE DRAWING 

side, the parting line of the flask being along a vertical plane 
running lengthwise through the middle of the cylinder. This 
permits the chest flanges to draw nicely, likewise the ribs on the 
foot, and allows the thin curving port cores to stand edgewise in 
the mold. 

Another method of molding would be with the valve seat down. 
This would involve loose pieces for the chest flanges, and setting 
of cores for the cylinder foot. It would, however, assure sound 
metal beyond question at the valve seat. Spongy metal at the 
important wearing surfaces, the valve seat and cylinder bore, is not 
permissible in any case, and care in molding and good design are 
necessary for good results. 

All corners must be carefully filleted, and chunks of metal 
must be avoided, especially where several walls or ribs join. The 
metal must be kept of average uniform thickness, so that the whole 
casting will cool uniformly. 

Machining Steam Cylinder. The boring may be done on a 
vertical boring mill, the heavy arm carrying the tool being thrust 
down unsupported into the cylinder, the latter being rotated by 
the table to which it is clamped. If the horizontal boring machine 
is used, the hole through the inside head for the stuffing box must 
be large enough to permit a stiff boring bar to be passed through. 
This allows a support at each end of the bar, to take the strain of 
the cut. 

The plane surfaces may be finished on a reciprocating planer 
or a rotary planer. In the latter case it is desirable to keep all 
lugs or projections back from finished surfaces, in order to permit 
the large round head which carries the cutters to pass over them 
without interference. 

The drilling of standard machine parts of this character is 
usually done through jigs, or plates carrying hardened steel bush- 
ings laid out to correspond with the holes required, and through 
which the drill is guided. These plates are located by some fixed 
line or lug on the casting, and then clamped fast, thus assuring 
exact duplication and rapid drilling, and avoiding the tedious laying 
out of the holes. In order to save changing the drill, it is desirable, 
if possible, to maintain the same size of hole on any given surface. 
Of course it is not always admissible to do this. 



MACHINE DRAWING 171 

PLATE B. STEAM CYLINDER 

After the exact and complete development of the steam-end 
layout, the student should be pretty thoroughly acquainted with 
the details of the cylinder. All the work thus far has been entirely 
for his own information, to get his ideas in visible shape, so that he 
himself can have a permanent record of them. This layout, how- 
ever, is not in suitable form to finish up into a detail drawing. Its 
sketchy nature and the confusion of parts, especially if attempt were 
made to add dimensions, would render it somewhat difficult to be 
read by a workman taking it up as an unfamiliar subject. Hence 
it is now necessary to separately detail the parts, with the object in 
view of transferring, in the simplest and most direct manner, specific 
information to the workman which will enable him to construct the 
several parts. It is not enough now that the drawing be clear to 
the man who makes it; it must be absolutely clear to the shop 
mechanic, who has no means of knowing the designer's plans except 
through the information which the drawing gives on its face. 

This requires that the draftsman should put himself in the 
workman's place, and forestall, by the explicit nature of his draw- 
ing, all possible questions which may arise in the shop. In this 
way only can he hope to avoid errors of construction and the con^ 
tinual annoyance of endless explanation of his orders. 

Size of Plate. Plate B is to be a finished drawing, and the first 
thing to do is to lay out the sheet. The standard sheet for details 
which has been adopted is 18X24 inches trimming size, with |-inch 
margin all round, so that the working space is 17x23 inches. The 
rectangle for the title is to be laid off 2|X4 inches in the lower right- 
hand corner, and must never be altered, either in size or position. 
This does not mean that other sizes are wrong, but once a standard 
system is adopted it must be strictly adhered to, both for artistic 
and commercial reasons. The scale to which the drawing is to be 
made is indicated in the title corner on every plate. 

Scales to be Used. The scales permissible for shop drawings 
in the United States are those readily derived from the common foot 
rule, such as full size, 6 inches = 1 foot, 3 inches = 1 foot, 1 J inches 
= 1 foot. These are the most common, most easily read from an 
ordinary scale, and one of these can usually be adopted. The 
student should learn to read these from an ordinary scale without 



172 



MACHINE DRAWING 




MACHINE DRAWING 173 

being confined to a special graduation. To do this it is not neces- 
sary to divide each dimension by 2, 4, and 8 to get half size, quarter 
size, or eighth size, and then lay down the result. For half size, or 
6 inches = 1 foot, f inch on an ordinary rule represents 1 inch. 
Hence, each half inch may be read as 1 inch, and its subdivisions 

0.1 2 

accordingly, thus : For 3 inches = 1 foot, or quarter 

lllllll'lllll l l ll 12 3 

size, \ inch represents 1 inch, and looks thus : i I i 



For 



1 J inches = 1 foot, or eighth size, f inch represents 1 inch, and looks 



thus: 







Nihil 



It is very easy to get accustomed to this, and 



it saves much time and trouble hunting up a special scale every time. 

The other allowable scales, less common, but sometimes neces- 
sary on large work, are 1 inch = 1 foot, f inch = 1 foot, \ inch = 1 
foot, | inch = 1 foot, \ inch = 1 foot, and \ inch = 1 foot. To use 
these scales conveniently, special graduation is desirable. 

Blocking Out Plate. The general arrangement of the sheet, 
number of views, and approximate space occupied, should be blocked 
out first. This can easily be done from the original layout. In 
general, several cross sections are preferable to a single view, which 
involves many dotted lines. Dotted lines are very convenient for 
showing invisible parts of an object, but they are often abused, and 
the drawing of a complicated piece made indefinite and confused 
thereby. As already stated, a working shop drawing is solely to 
convey information to the workman at the least possible cost. A 
tareful consideration of this will settle the question of the number of 
views necessary, their character, and the amount of dotted line 
work desirable. 

Never let the drawing become the master; always be master 
of the drawing. Do not draw an extra view if no use can be seen 
for it. Do not put in dotted lines if the detail is completely shown 
without them. Full lines, or lines which show visible portions, 
must, of course, be shown completely. 

Practice of Checking Dimensions by Measurements. The 
nature of the pencil work on Plate B should be the same as on the 
original layout; viz, sharp, definite lines and positive intersections. 
Above all things learn the habit of accurate workmanship, for it 



174 MACHINE DRAWING 

will save many errors and a vast amount of time. The draftsman 
must check himself at every line he draws. Slight errors in scaling 
will often throw parts out of proper relation to each other, and inter- 
ferences, which the drawing does not show, will become apparent 
only when the parts get into the machinist's hands. 

It is dangerous practice to project across from one view to the 
other. It only takes a slight irregularity or spring in the T=square 
to vary the location of lines very perceptibly from where they should 
be, and once out of scale from this reason it is almost impossible to 
work a view with any certainty. Rather than project across from 
view to view, the principal lines, at least, should be scaled off on 
each view, and it will be found that in the end time will be saved 
and greater accuracy secured. 

Complete Development of Different Sections. It is not econ- 
omy of time to finish one view before beginning another. It is 
better to take some single detail of the drawing and develop it in all 
views, in order to study it from all sides. What is completed in one 
view may be found to be totally wrong when developed from another 
side, and the time spent on the first view will be wholly wasted. 
For example, in the present case the steam ports should be drawn 
in side elevation, end elevation, and plan, and when thus completed 
the mind can leave them and in a similar fashion take up the study 
of the flanges, then the cylinder foot, and so on. Thus again the 
draftsman is master of his drawing, for he is continually making it 
tell him whether he is right or wrong. If, on the contrary, he allows 
himself to look at but one side at a time, and works from that stand- 
point alone, it may lead him into many difficulties from which he 
cannot readily extricate himself. 

Do not be afraid to use the eraser. The draftsman who hesi- 
tates to draw until he is positive that no change will be necessary, 
is likely to spend the greater portion of his time in unprofitable 
dreams, for he is attempting the impossible. A drawing is a means, 
not an end; and, as has been already pointed out, it greatly assists 
the draftsman in clearing up many doubtful questions which the 
imagination alone cannot do. 

A bold attack of a problem shows the quickest path to its 
solution, even if lines must be erased again and again. It is a sign 
of serious lack of ability to hesitate in the use of pencil and eraser. 



MACHINE DRAWING 175 

Clearness of Drawings an Important Point. Attention is called 
to the simple, straightforward character of Plate B. Notice the 
almost entire absence of dotted lines; the enlarged section through 
the ports, giving ample opportunity for dimensions without con- 
fusion; the use of a half end elevation and a half cross section — the 
one to make clear the flange and bolt layout; the other to show the 
exhaust opening, the small auxiliary views (drawn at convenient 
points) of the exhaust flange layout, the cylinder foot, and the drip boss. 

A steam cylinder is a fairly complicated casting; and it would 
be an easy matter, by the use of elaborate views, the dotting in of 
parts already completely shown, and careless linework, to rob this 
drawing almost entirely of its clearness and directness of illustration. 
Just what is necessary (for clearness' sake) and no more (for cheap- 
ness' sake), is the whole matter in a nutshell, and is what determines 
its shop and commercial value. 

Dimensions and Letters. A good line drawing can be spoiled 
by poorly arranged dimensions and hasty lettering. The five prin- 
cipal points to be kept in mind to develop excellence in this respect 
are: (1) system; (2) accuracy; (3) clearness; (4) completeness; (5) 
character. 

System. The habit of system in placing figures and letters on 
a drawing is the one element which, to a large extent, controls all 
the others. If the systematic habit is established early, the other 
requirements will be fulfilled more easily. A haphazard method 
will, on the contrary, just as surely prevent the successful cultivation 
of the ability to figure a drawing. In fact, if the haphazard habit 
is continued it will itself, by the dissatisfaction which it causes, soon 
compel the draftsman to change his occupation. 

In the first place, whatever part of a machine detail is to be 
dimensioned, that particular part should receive attention until it 
has been^completely figured. Do not jump from one point to an- 
other, putting in a figure here and another there. Stick to one 
thing until it is done. 

For example, take Plate D and the simple detail of the steam 
pipe. Suppose we start with one of the square flanges. The first 
question is: "Where is this flange located?" This is answered by 
the dimensions 5-inch and 21 -inch centers, which refer the face of 
the flange to the center of the pipe and the flanges to each other. 



176 MACHINE DRAWING 

The next question is: "What are the three dimensions of the flange 
— length, breadth, and thickness?" This is readily answered as 
shown on the drawing. The next question is: "What further de- 
scription is necessary to completely specify the shape of the flange?" 
This is answered by the radius of the corners, f inch R. Next, 
"What drilling or special feature exists in the flange?" This is 
answered by \ J-inch drill, 3 J-inch centers, and the letter / to denote 
that the face is to be finished. 

The round flange of this pipe is approached and figured in 
the same way, except that the location of the face is preferably 
referred to the face of the square flange by the figure 8| inches, 
instead of to the center of the pipe, because the planer hand will 
more naturally use this figure. 

These flanges are now to be connected by a pipe involving 
two sizes. The main pipe is 3 inches diameter inside, 4 inches 
outside, and \ inch thick, running into the two branches by fillets 
and radii, as figured. The two branches are really one pipe, 2\ 
inches inside, 3J inches outside, J inch thick, and sweeping down 
into the square flanges by 4-inch radii. 

This systematic method takes longer to explain than to actually 
execute, but it is typical of the train of thought which must be 
followed on all pieces, simple or complicated, in order to properly 
place dimensions. 

In general, it may be stated that all parts of a piece must be 
referred either to each other, or to some common reference line, or 
to both. Each part so referred must then be figured as a piece by 
itself, and then its connections to the principal structure. Thus, 
figuring a machine detail involves three things: (1) relative location 
of its parts; (2) proportions of these parts; (3) proportions of con- 
necting members. 

As in the original design of a piece, so in the figuring of it the 
draftsman must as far as possible put himself in the place of the 
workman, judging the methods and processes of construction and 
available tools. This will largely influence the arrangement of the 
dimensions. Of course it implies considerable experience in shop 
work, which some students do not possess. He can begin none too 
early, however, to learn to look at his work from the shop stand- 
point, and surely make it some better on that account. 



MACHINE DRAWING 177 

Pieces must not only be systematically dimensioned, but 
regularly specified and called for by suitable titles. 

A title should specify at least three things: (1) name of piece; 
(2) number wanted for one machine; (3) material. 

To these might be added a fourth; viz, pattern or piece number. 
The latter is not specified on the drawings under discussion, because 
systems of pattern and piece numbering are so varied that little 
would be gained by developing one for this special study. 

These titles should always be put on in the same way, as the 
workmen become used to a certain system and are likely to mis- 
understand directions if a regular plan is not followed. A good 
way to arrange titles is suggested on the plates, although there 
are others which might be used. ' 

Bolts are usually specified by diameter and length under the 
head, the length of thread being determined by some standard 
system in use by the shop, unless otherwise called for. Bolts are 
specified on the sheet containing the piece into which they are tapped. 
In the case of through bolts, tapped into neither piece, they are 
preferably called for in connection with the principal member. 

Accuracy. Of course the dimensions on a drawing must be 
accurate. It is, however, a very easy matter to make errors. To 
insure accuracy a figure must never be put down carelessly, and a 
constant watch must be kept that scaled figures add up to over-all 
dimensions. It will not do to rely upon scaling alone, as a very slight 
variation from exact scale may throw two dimensions out with each 
other. In spite of all the care that can be exercised errors will 
creep in, and a final thorough checking must be given a drawing 
before it is pronounced complete. A good rule to follow in checking 
up is to "assume everything wrong until it is proved to be right." 

Clearness. As in the line drawing itself, there must be abso- 
lute clearness of instruction by the dimensions. Any doubt as to 
what a figure is, or what it means, rules out that figure as part of 
the drawing. If a piece is made wrong because doubt of this char- 
acter is transmitted to the workman, the draftsman is always held 
responsible for the error. 

Figures should, in all cases, be placed where they can be most 
clearly read. They should be bunched on a single view as far as 
possible, but not when greater clearness demands that another view 



178 MACHINE DRAWING 

be used. It hinders the reading of a drawing materially if the eye 
is forced to jump over large spaces of the sheet from view to view, 
to catch the several dimensions of a small detail. Usually it is easy 
to so group figures as to avoid this. 

It is a good plan to keep dimensions off the body of the draw- 
ing, when it can be done so conveniently. It is not worth while, 
however, to go out of one's way to do this, as figures in the open 
spaces of a detail do not at all destroy its clearness. 

Extended notes on a drawing to make it clear should not be 
required, but they should be used without hesitation if any doubt 
exists. An explicit note of instruction is the final resource for 
clearness when the art of drawing fails of its purpose, as it some- 
times does. 

Completeness. A detail is completely dimensioned when it 
shows all the figures necessary for the workman. Anything short 
of this is incompleteness. As modern shops hold the draftsman 
solely responsible for the design, the mechanic is not allowed to 
modify it by filling in any omitted dimensions. The only way to 
be sure that all the dimensions are on is to systematically go all 
around a piece inside and out, according to the method suggested 
under the paragraph on "System". 

It is a good plan to always bear in mind that not only the 
machinist is to use the drawing, but also the- pattern maker. For 
the benefit of the latter, special attention is desirable in figuring 
the cores. This saves him some addition and subtraction. In 
general, it has been found that less chance of error exists if mathe- 
matical work is not required of the shopman, all necessary data 
being furnished on the face of the drawing. 

Character. By character in figures and letters is meant uni- 
form style, height, and slope, and a certain boldness peculiar to the 
work of the expert draftsman. The last is difficult for the novice 
to acquire. The student should not be discouraged because his 
efforts do not look like impressions from printers' type. Artistic 
excellence is the result of long experience, but is based on character. 
If the student can once get character into his work, the artistic 
feature will, with careful and constant practice, gradually develop. 
It is safe to say that there is no one element of a drawing which 
more positively stamps it as the work of an amateur than the char- 



MACHINE DRAWING 179 

acter of the lettering, and every attention should be paid to getting 
out of the apprenticeship stage in this respect. Freehand lettering 
only is permitted in the drawings illustrated herewith. Ruled 
letters are seldom found on any working drawings, as the element 
of time involved is so great that few shops are willing to pay for it. 

Uniform style requires that if capitals only are used in titles, 
they only must be used in notes and elsewhere on the drawing. If 
lower-case letters are used, they must be used in every part of the 
drawing. One style should not be mixed with another. The height 
of the letters should be limited by two horizontal lines, and though 
practice may render the upper line unnecessary, it takes but an 
instant to draw it, and uniform height is then assured. A good 
height for titles of details such as are illustrated is ^ inch. The 
height once chosen should be adhered to throughout the whole set. 
A medium, not a hard, grade of pencil (3H) will give the hand 
greater freedom. A great temptation exists to omit titles from the 
pencil drawing, simply inking them on the tracing. This is false 
economy of time, for in the end it will be found that enough time 
will be saved by the certainty with which the tracing can be made 
to more than pay for the labor on the pencil drawing. Again, it 
permits the tracing, in regular shop practice, to be made by cheaper 
labor than that which produced the pencil drawing. 

Uniform slope is most easily acquired by the use of guide 
lines put in at "frequent intervals. A small wooden triangle can 
be made, giving the required angle. The angle of the letters shown 
on the plates is 9 degrees, or about 1-inch slope in 6 inches. The 
question as to whether letters should incline backwards, forwards, 
or stand vertical, does not enter this discussion. Character is not 
affected by the slope. The student may choose whatever comes 
most natural to him, but having chosen, the character of his work 
will be spoiled if he varies it. The most difficult of the three is the 
vertical style; hence most draftsmen incline their letters. The 
backward slope is used on the plates of this shop drawing paper, 
thus giving the student opportunity to compare with plates in the 
earlier books, and follow his preference. 

The effect of change of style, height, and slope is shown in 
Fig. 122. Attention is called to Fig. 123, which is a sample title, 
in which these points are corrected. 



180 



MACHINE DRAWING 



Principal Titles. The principle title of a drawing should con- 
tain at least seven items: (1) name of principal details shown; (2) 

name of machine; (3) firm name 



sih am r,vi mnm ~ 



STIiAM C Y\\N\)F P ~ 
\6-tt^-\g DUPLhX PU^W 




Fig. 122. Sample Titles Showing Effect of 
Non-Uniformity of Lettering 



and location; (4) scale of draw- 
ing; (5) date of completion; (6) 
draftsman's signature; (7) filing 
number. 

To these are often added 
others, but for purposes of filing 
and reference the above at least 
must be put on. The filing num- 
ber may or may not be put in 
the title frame, but it is really a 
part of it. It is often put in the margin below the title. 

An arrangement of title should be established and then followed 
exactly, without variation either as to location on sheet or detail 
make-up. Abbreviated words are always permissible in titles, 
provided the meaning is clear. Special care must be taken in 
punctuation, however, as a title, whether abbreviated or not, has 
an unfinished appearance if the periods, commas, and other necessary 
punctuation marks are not included. 

The sample title illustrated in Fig. 123 indicates the arrange- 
ment chosen for the drawings of Part I. Note that in this special 




Fig. 123. Sample Plate Title Properly Drawn 



case the residence of the student draftsman has been substituted 
for the file number of the drawing. 

This style of title must be put with care on every drawing, 



MACHINE DRAWING 181 

even on the rough pencil layouts. In the latter case it may of 
course be left in pencil, as the rough layouts are not to be inked. 

Inking and Tracing. Both bond paper and tracing cloth are 
used in business practice for finished drawings. It is desirable to 
keep a stock of both in any drawing office, so that either may be 
used as occasion requires. Bond paper stretched on the board 
gives a beautiful surface to take the ink, and very handsome and 
effective detail or assembled drawings can thus be produced. 

Changes are not quite as readily made on bond paper as on 
tracing cloth, and it takes a little longer to make the blue print. 
In other ways the bond paper is not quite as flexible to use as the 
tracing cloth. However, one must be guided entirely by shop con- 
ditions to settle the question of preference. As the tracing cloth is 
generally used, and suits the purpose of the student better, it will 
be required in this work. 

Preliminaries. The inking should be done on the rough side of 
the cloth. One reason for choosing this side is that as the cloth 
tends to curl under toward the glazed side, the drawing as it lies 
right side up will tend to straighten itself. This seems to be a small 
point, but it is a very important advantage for filing and for the 
convenience of those who are to handle the drawings. Also the 
rough side takes colors and inks better than the glazed side. To 
trace on the glazed side is not wrong, for it is often done, but it 
possesses no advantages of its own, and has the disadvantage men- 
tioned above. 

Chalk dust scattered over the surface of the cloth after it is 
tacked down will remove the slightly greasy coating which prevents 
the ink from flowing well from the pen. This is always necessary 
if the glazed side be used, and usually for the rough side. The 
chalk must be carefully removed from the cloth before inking. 

Rules for Inking. The first step in inking is to draw the center 
lines. Remember that accurate intersections are of the utmost 
importance. No circle is complete without two intersecting lines, 
preferably at 90 degrees, to determine its center, and these lines 
should be inked before the circle. When this is done, a definite point 
exists for the needle point of the compasses. If the circle is drawn 
first, the needle point may not be placed accurately at the center on 
the pencil drawing beneath, thus throwing the location out. 



182 MACHINE DRAWING 

Likewise the principal center lines of pieces, the lines around 
which the pencil drawing was built up, should be at once put in. 

The main body of the drawing, the full lines, should be taken 
next. In general, circles and arcs should be inked first, but there 
are cases where it is easier to run the arcs into the straight lines 
than to match the straight lines to the arcs. These are exceptions, 
however, and can be judged only as the case arises. 

Straight lines, horizontal and vertical, should be inked with 
the T-square and triangle in position. It is a common practice to 
dispense with the use of the T-square entirely in inking in, using 
the triangle to match the lines to the arcs already drawn. A neces- 
sity for this implies very poor work on the arcs, for with any reason- 
able care true horizontal and vertical lines will match the arcs all 
right. With regard to time required, the accuracy with which the 
T-square may be brought up to a line, or the triangle set on the 
T-square, more than makes up for the time gained in even an approxi- 
mate setting of the triangle without a guide. It is just as easy 
to cultivate the habit of holding the T-square and triangle with the 
left hand and the pen with the right, and draw an exact line, as to 
lapse into the other method, which is not workmanlike. 

The lines of the body of the drawing depend for their width 
upon the size of the detail. For a large piece they may be ^ inch 
wide, and the shade lines ^ inch. For a small detail such widths 
would be too great. Remember that contrast is the principal aim, 
and to produce it is the only reason why we use different kinds of 
lines on a drawing. Hence the greatest care must be exercised to 
prevent body lines from becoming confused with center or dimen- 
sion lines, and vice versa. Also thick lines are desirable for the 
production of a bold blue print. 

Shade Lines. Shade lines certainly improve the drawing from 
an artistic standpoint, and the student has been shown in Machine 
Drawing, Part I, how to put them on when desired. Whether or 
not it is desirable to adopt them on all working drawings is not the 
purpose of this book to decide, or even discuss. Almost always 
drawings can be made perfectly clear without them, and are so 
made and satisfactorily used in probably the majority of shops. 
Some shops are willing to pay for the extra time necessary to put on 
shade lines; this, however, is purely their own investment. 



MACHINE DRAWING 



183 



Crosshatching. Cross-section lines are usually drawn at an 
angle of 45 degrees with the horizontal, and on sections which are 
adjacent to each other the slope should be in different directions. 
If three or more sections come together, the width between section 
lines can be so changed as to indicate clearly the different parts. 
An example of this is shown in Fig. 124. 

The spacing of section lines must not be too fine, rarely closer 
than rs inch, more often from ^ to § inch, else the labor involved 
is too great and uniformity practically impossible. It is a waste 
of time to rule in section lines on the pencil drawing; they may be 
sketched in freehand, as shown on the original layout of the steam 
cylinder. Even spacing concerns the tracing alone, and the 
student should train his eye to regularity as he traces. The thick- 
ness of section lines may be intermediate between that of center 
lines and the body lines of the drawing. 

Inking Dimensions and Letters. Ex- 
tension lines may be dotted, as explained 
in Mechanical Drawing, Part III, or 
they may be fine, full lines, the latter 
method being illustrated in the series of 
pump plates in this paper. Dimension 
lines are also often made fine, full lines. 
If these lines are made full they should 
be made as fine as it is possible to draw 
them and still have them firm, clear lines. 
The same width should be used as for 
center lines. 

Character in inked figures and let- 
ters is more difficult to attain than in 
pencil work. In the first place a pen 
suitable to the style of drawing is necessary. A civil engineer's fine 
mapping pen, which gives character to his drawing, is not desirable 
in producing the bold character of a machine drawing. For the latter, 
choose a rather stiff, blunt pen which is not "scratchy," but runs 
smoothly, making a line of uniform width. A pen with a round, 
or ball-shaped nib, now on the market, answers the purpose well 
for ordinary details. A bold, free stroke should be made with the 
idea of producing a smooth, even line, finished at the first trial. The 




Fig. 124. Section Showing Varia- 
tions in Crosshatching 



184 MACHINE DRAWING 



jj 



hesitating uncertainty of the beginner's hand produces a "shaky 
letter, and going over a letter or figure twice or more to smooth it 
up usually makes it worse. 

Figures and letters which are broad in proportion to height 
are easier to make, and have more character. It should never for 
a moment be forgotten that uniform height and slope carefully 
followed will develop character and quickly lead to artistic 
excellence. 

Foot and inch marks are often put after figures according to 
the common usage. In cases where feet and inches are expressed, 
thus: 3'-6", or 4'-0", they are, of course, absolutely necessary, and 
the dash between the figures must be very positively indicated. In 
cases of inch dimensions alone the marks may be put on if desired, 
but where there can be no doubt that inches, and not feet, are meant, 
the inch marks are not necessary. 

Abbreviations. A list of the most common abbreviations in 
use on working drawings follows. This list has been adopted for 
the plates in Machine Drawing Part I : 

F. A. O finished all over. 

/ finished surface. 

R. radius. 

D diameter. 

R. H right hand. 

L. H . . . left hand. 

P. R piston rod. 

P. TAP pipe tap. 

CTRS centers. 

C. I cast iron. 

S. C steel casting. 

Bz bronze. 

C. R. S cold rolled steel. 

T. S. . . . tool steel. 

O. H. S open hearth steel. 

W. I. . wrought iron 

PLATE C. PISTON ROD AND VALVE STEM 

Specifications. The piston is of the one-piece box type, with 
sprung-in rings. The width is reduced to 4| inches at the outside, 
so that if the piston strikes the cylinder heads it will not tend to 
spr'ng and break off the narrow ridge of metal outside of the packing 
ring. The piston rod is fastened to the piston on a taper drawn in 



MACHINE DRAWING 



185 




186 MACHINE DRAWING 

by a nut, and the nut is checked by a J-inch split pin. The packing 
rings are prevented from slipping round the piston by lugs fitting 
loosely in chipped recesses in the groove. These being at opposite 
sides for each groove, the leakage of steam through the split in the 
ring is minimized, for it must pass halfway around the piston before 
it can pass through the split in the other ring. This is a simple, but 
fairly effective, device. 

The packing rings are usually cast in the form of a cylinder 
of some length, turned to a diameter a little larger than the cylin- 
der bore, cut off to the required width, and sufficient space cut out 
to permit being sprung in to the size of cylinder bore. 

The location of the spool on the piston rod is not positively 
known, as the setting of the valve bracket may be slightly differ- 
ent from what the drawing calls for. Hence, instead of a dimension, 
the words "measure for" are put on, to indicate that the spool be 
located during the erection of the pump. The hexagonal flanges of 
the spool are convenient to hold the rod from turning while screwing 
on the piston and plunger nuts. 

Molding and Machining. There are no special features con- 
nected with the molding and machining of parts on Plate C. The 
holes in the piston side walls are necessary to give supports for the 
core, the piston being cast on its side. These holes, after the core 
is cleaned out through them, are plugged as indicated. 

PLATE D. STEAM CHEST AND VALVE 

Specifications. The steam chest in this instance is located on 
the cylinder by fitting down over the ledge made by the valve seat. 
The side flanges also serve the purpose of guiding the valve. It will 
be noticed that the steam-chest cover is 15J inches X 11J inches, 
while the steam chest is 15 inches X 11 inches. This allows a ledge 
of i inch, all around which the cover overhangs the walls of the 
chest. The steam cylinder flange in order to correspond must like- 
wise be 15| inches X Hi inches. The reason this is done is because 
of the difficulty of making good matched joints between the cylinder 
flange, chest, and cover. The practice of thus leaving a little ledge 
all around is by no means universal, and often the irregularity in the 
joints is smoothed off by chipping. This is the case with the other 
flanges on this pump. The steam chest, however, was thought less 



MACHINE DRAWING 



187 




188 MACHINE DRAWING 

likely to match properly, and the slight overhang gives the finished 
appearance of a sort of beaded edge. 

The valve is what is known as a "square" slide valve. This 
means that when the valve is placed central on the ports its work- 
ing edges are "square" with the ports; that is, in exact line with 
them. If the valve be moved either way from this position, the 
slightest travel will admit steam to one end of the cylinder and 
exhaust -it from the other. (See Plate A.) Another way of stating 
this is to say that a "square" slide valve is a slide valve without 
"lap". 

The valve is driven from the valve stem by the striking of 
the nuts against the lug on its top. Since the valve is already 
guided on its edges by the steam-chest flange, the valve stem, to 
avoid springing, must be perfectly free in the slot cast for it, as is 
shown by the f-inch radius of the bottom, the stem being 1 inch in 
diameter. 

The steam-pipe flange is made square to keep the height of 
the chest as low as possible. The radius of the bend should be 
ample; in this case 4 inches is considered sufficient, 

The exhaust tee must have its upper flange high enough so 
that the chest cover can be lifted and slipped off the studs without 
interfering with it. The lower flanges should be made wide enough 
to permit the tap bolts to be put in without striking the 4-inch 
vertical pipe, 5-inch centers being necessary. The i-inch drip-cock, 
as located, readily drains the steam chest and exhaust passage of 
both cylinders, as well as the exhaust tee. 

Molding. It is evident that the steam chest will be molded 
in the position shown on the drawing. The parting line of the 
mold will be through the centers of the steam-pipe opening and 
the stuffing-box. These holes must be cored out. The main body 
of the chest could be made to leave its own core, but it may not 
be made in this way. It may be cheaper to fashion the -pattern 
solid, and make one large core-box for the inside. In this way 
the pattern will probably hold its shape better and require less 
repairs, than if it were made in green sand. The core-box will be 
an extra piece to make, but it probably will cost no more than to 
carve out the inside of the pattern, and is a rather more substantial 
job when done. The molding can be satisfactorily done by either 



MACHINE DRAWING 189 

method, shop conditions being the controlling element. As far as 
the labor of molding alone is concerned, the first method is prob- 
ably easier, as it saves handling large cores. 

The other parts in Plate D are very simple in their molding, 
and require no special attention. 

Machining. Most of the surface work on this plate is adapted 
to the planer. The slide valve may, perhaps, if finished in lots of 
considerable number, be more satisfactorily handled on the milling 
machine. The final finish of the face of the valve must be a scraped 
fit to its seat. 

The drilling of the cover and pipe flanges is to actual layout 
on the casting, or preferably, through jig plates. A templet for 
laying out is at least desirable, even though the expense of a jig 
plate be not deemed necessary. 

PLATES E AND F. VALVE MOTION LAYOUT 

General Specifications. These plates represent the layout of 
the valve motion, and are necessary in order to find the length of the 
levers and rocker arms. It will be noticed in Plate F that the valve 
stem of one side of the pump is controlled by the movement of the 
piston rod of the other side, the proper direction of motion being 
given to the valve by placing the rocker shaft above or below the 
valve stem as required. By reference to Plate A it will be further 
noticed that the nuts on the valve stem inside the chest, which abut 
against the faces of the lug on the valve, do not rest against the 
faces of the lug in the position shown, but have considerable lost 
motion. This lost motion is one of the essential features of the 
valve motion of a duplex pump, and permits the valve to remain 
at rest for a short period at the end of the stroke, though the valve 
stem may have reversed its motion and begun its return stroke. 
When this lost motion is taken up by the movement of the stem 
and the nuts abut against the lug on the valve, the valve will move, 
and from this point to the end of the stroke be positively controlled 
by the motion of the stem. At the end of the stroke the stem will 
reverse, when the lost motion will again permit the valve to rest for 
the same period as at the other end, and then move on as before. 
The time of rest of the valve, and consequently the pistons and 
plungers, is approximately one-third the period of the stroke. This 



190 



MACHINE DRAWING 




MACHINE DRAWING 



191 




192 MACHINE DRAWING 

means that the piston on one side travels one-third of its stroke 
before it picks up, through the valve levers, the valve on the other 
side. During the second third of its travel it is bringing the valve 
to the point of opening. During the last third of its travel it is 
opening the port, wider and wider, to steam. Thus the opposite 
piston will start when the first piston has covered two-thirds of its 
stroke, and there will be only one-third of the stroke when both 
pistons are moving at the same time. 

This relative period of rest to motion is not always made in 
this exact ratio, but is at least approximate to it. The period of 
rest at the end of the stroke is to allow the water end to adjust 
itself quietly to the reversal of motion about to take place at the 
end of the stroke. When the plunger stops, the water valves must 
be given time to seat themselves, and the flow of water through 
the passages checked. It is much easier to start the flow in the 
opposite direction if the reversal of plunger motion is not instan- 
taneous. Hence for handling long columns of water, which, once 
in motion, tend by considerable energy to remain in motion, the 
duplex pump by this peculiar delayed action has been found to be 
well suited. 

Travel of Valve Stem. It will be found that for complete 
uncovering of port, and motion divisible into thirds as described, 
the travel of the valve stem should be three times the width of port, 
or 3 X | = 2f inches. A little more than this is allowed, and the 
travel made 2J- inches in this case. Referring to Plate E, this dis- 
tance is laid off as shown by the two limiting vertical lines across 
the line of the valve stem, the central vertical line of mid-position 
being drawn. The problem then is to find such centers for the 
rocker arms that the travel of the piston-rod spool will, through 
proper leverage, produce travel of the valve stem between these 
two vertical lines. This can readily be done by a few trials, the 
only requirement for this case being that the extremes of the arc 
of swing of both piston-rod lever and rocker arm shall be equally 
above and below the center of piston rod and valve stem, respec- 
tively. The greatest possible travel of the piston-rod spool, 12 \ 
inches, is usually laid out in this case, not the nominal 12 inches. 

Length of Levers and Arms. From this layout the lengths of 
the levers and arms may be scaled off for the detail drawing, also the 



MACHINE DRAWING 193 

location of the rocker-arm centers. The student has the former 
given him on Plate G, but the latter, which is necessary for the 
development of Plate H, must be determined by his own layout. 
Plate F must also be laid out before developing the cross section of 
the valve bracket. 

Stuffing Boxes. The design of stuffing boxes for both steam 
and water ends, and the length of the yoke, should be determined 
next. A safe method of assuming clearance between the spool and 
the gland studs at the end of the stroke is to imagine that the gland 
stud nuts have accidentally worked off the studs, so that they are 
about to drop. They are thus shown by dotted lines on Plate E. 
A good clearance, say \ inch to J inch, is then allowed, and the gland 
drawn in. The length of the gland is determined by the number 
of rings of packing necessary in the stuffing box; it is usually pro- 
vided that the gland may compress the packing to about one-half 
its original depth before bringing up against the face of the box. 
Packing f-inch square will do for this size of piston rod, hence the 
faces of the yoke are easily determined, and its detail, with the 
stuffing boxes, proceeded with as on Plate H. The length of yoke 
may be brought to an even figure; and proceeding on the above 
plan the length can be conveniently made in even inches without 
any fractions; viz, 28 inches. 

It will be noticed that the stuffing-box flanges serve to centei 
the yoke in line with the steam and water cylinders. This is a 
desirable feature of construction, and forms a simple and easy 
method for lining up the steam and water ends. 

PLATE Q. VALVE MOTION DETAILS 

Piston=Rod Levers. The piston-rod levers on this plate are 
specified to be steel forgings. Forgings of this kind are expensive, 
but are light, neat, and reliable for the important service which they 
have to perform. Castings, whether steel or iron, are much cheaper, 
and perhaps more commonly used for this detail. When sound 
they are equally serviceable, though of more clumsy proportions; 
but the danger in castings of this form is the existence of hidden 
flaws or pockets, which frequently occur at the points where the 
hub or the fork joins the arm. These flaws cannot be readily 
detected from the outside, and breakage may occur at some 



194 



MACHINE DRAWING 




MACHINE DRAWING 195 

critical time, when the disability of the pump may be a serious 
matter. 

Dimensions "Out of Scale". It will be noticed that on the 
detail of the "link pin" two of the dimensions have a short "wavy", 
line beneath the figures. This is one of the several ways of indicat- 
ing that the dimension is "out of scale". Some draftsmen use a' 
straight dash beneath the figure; some draw a circle about it; some 
print after the figure, "out of scale". Although workmen are not 
allowed to scale drawings, but are required to "work to figures only," 
yet for general safety's sake, and for the sake of the draftsmen who 
consult the drawings frequently, attention must be called to any 
variation of the figure from the measured distance on the drawing. 
Nothing makes a workman, or any one else who reads a shop draw- 
ing, lose confidence in it more quickly than to discover that it does 
not "scale" ; but when no indication exists that the draftsman 
himself is aware of it, then every dimension is viewed with doubt 
and hesitation, and the drawing becomes practically worthless. 

Dimensions seldom should be out of scale; but if they are, through 
error or necessary change, a carefully worded note should be added. 

Molding and Machining. No special features of molding or 
machining are noteworthy on Plate G. 

PLATE H. YOKE, STUFFING BOXES, BRACKET, ETC. 

Having worked up the layouts of Plates E and F, the student 
has enough information to proceed with Plate H. This, like Plate 
B, is without dimensions, the student's work being to make the 
drawing and fill in the necessary shop data. 

Specifications. The valve-lever bracket is bolted down to its 
lug on the yoke through holes larger than the bolt, thus permitting 
slight adjustment. When the proper location is determined, the 
bracket is positively fixed in position by two dowels, \ inch in diam- 
eter. The holes in both bracket and yoke are drilled through both 
pieces at the same operation. This very common method of fixing 
bolted parts of machinery in absolute position not only assures 
firmness, but also in case of removal, permits the part to be readily 
and positively replaced in its exact original position. 

If possible, the steam cylinder cricket should be of such height 
that the stone or brick work upon which it rests shall be at the 



196 



MACHINE DRAWING 




MACHINE DRAWING 197 

same level as that beneath the water cylinder. The tapped holes in 
the top surface receive bolts from the cylinder foot. These bolts 
are often used only for shipping purposes, the cylinder foot when 
the pump is set up being allowed to slide freely on the cricket, thus 
permitting free expansion and contraction. In such cases the water 
end is rigidly fastened to the foundation by holding down bolts. 

Molding and Machining. The valve lever-bracket would 
most naturally be molded with the axes of the shafts vertical, the 
parting line of the mold being the center line of the middle web. 
This makes quite a long "draw" for the shaft bosses, but the ample 
taper on the outside overcomes this difficulty. The space between 
the side webs leaves its own core. The shaft cores stand on end in 
the mold, which is the best position for strength and stability. 

Another method is to have the parting line of the mold on 
the vertical center line of the bracket, as shown in the end view. 
In this case the bracket would be cast on its side, and cores must be 
set for each side of the middle web. The shaft cores are set as 
easily as before, but in this case lie flat. As with the steam chest, 
each method has its advantages, which depend largely upon existing 
conditions. As cored work is generally avoided whenever possible, 
the first method would probably be chosen. 

The shaft bosses are "chamber-cored, " to save labor in boring, 
the bearing surface for the shaft being only a short distance at the 
ends. The chamber-core diameter should be enough larger than 
the shaft so that by no possibility can the cutter run into the rough 
scale, even if the hole be bored slightly out of line. If it should do 
this, the labor of caring for the cutters more than offsets the attempt- 
ed saving of labor. 

The yoke is simply a barrel open at each end, and with a piece 
cut out of its side. The inside evidently must be cored out, and 
the core is satisfactorily supported at the ends on its horizontal 
axis. The parting line of the mold may be either the vertical or 
horizontal axis of the end view, the only difference being that in 
one case the ledge for the valve bracket will "draw," and in the 
other case it must be loose on the pattern and "pulled in" after the 
main pattern is drawn. 

The cricket and stuffing boxes present no difficulties. The bore 
of the stuffing boxes and glands should be from ^ inch to tb inch 



198 



MACHINE DRAWING 




MACHINE DRAWING 199 

larger than the rod, to allow the fit to be entirely between the rod 
and the packing. 

The horizontal boring machine with a double facing head is 
adapted to boring and facing the yoke flanges. The drilling is 
accomplished as before by templet or jig. 

Attention is called to the tapped holes for oil or grease cups 
on the valve-lever bracket. The holes on the lower boss cannot 
be drilled strictly as shown, because the drill shank will not clear 
the upper boss. They should be swung around the boss at such 
an angle as will allow the drill to clear. This is a good instance of 
the common error of drawing details which cannot be made, and 
constant watch must be kept to avoid such mistakes. 

PLATE I. WATER END LAYOUT 

Specifications. In the preceding work, the completed plates 
were used to assist the student in developing the layout drawings 
for other parts of the pump. In this Section, Plates K and L„ being 
given in full detail, offer a good start for the development of the 
water cylinder, which is the purpose of Plate I. As before, work 
should begin at the inside and progress outwards. Thus the piston 
rod with its nut should be drawn first, the hub of the plunger built 
around it, then the plunger barrel, the bushing, and ring to clamp 
the bushing. The limits of the plunger travel should be sketched in, 
and the valve outline shown, in order to determine clearances. The 
progress of Plate I is on exactly the same basis as that stated in 
detail for the steam cylinder layout; hence it need not be repeated. 

Plunger and Bushing. The points controlling the design of the 
water end must, however, be studied to enable the student to work 
intelligently. The fit of the rod into the plunger hub is loose, A -inch 
play being allowed, in order to permit the plunger to be guided solely 
by its bushing, and thus be independent of any change of alignment 
of the piston rod. 

The relative length of plunger and bushing should allow the 
end of the plunger to overrun the edge of the bushing at the ter- 
mination of the stroke, to prevent the formation of a shoulder. 
The bushing is made of brass because of the better bearing of the 
two dissimilar metals, brass, and iron. Of course there is no lubri- 
cation except the water, and the dissimilar metals tend to "cut" 



200 MACHINE DRAWING 

less than if both were alike. The brass bushing also prevents the 
plunger from "rusting in" in case of long periods of disuse. The 
bushing being of expensive material is made as light as possible, 
hence it has no stiffness of its own. Therefore, it is reinforced by a 
deep cast-iron ring, which also takes the bolts and clamps the bush- 
ing tightly to its ground seat. These stud bolts are usually made 
of "tobin bronze," a rust-proof material, possessing strength almost 
as great as that of steel. This arrangement permits ready removal 
of the bushing when necessary. 

Hand Holes. As the parts of the common pump valve illus- 
trated in detail on Plate L must be often replaced during service 
of the pump, provision must be made for unscrewing the stem and 
substituting a new one. This must be done through the hand holes 
provided on the cylinder. The lower valve deck must be located 
so that the inner valves when unscrewed will not strike the clamp 
ring. As shown in Plate I, the clearance is pretty small, almost too 
small, but as it affects only two valves, it will probably cause no 
inconvenience. No hand holes are necessary for the end chambers, 
as access to the valves is had by removing the outer heads. 

Deck Details. The upper deck may be placed at a height 
giving sufficient clearance to allow the upper nuts of the clamp ring 
to be unscrewed with a socket wrench from the end of the pump: 
These decks are subjected to a severe pounding from the pulsations 
of the pump, and should be amply strong; If inches is deemed thick 
enough for this case. 

The middle transverse wall may be 1J inches thick and the 
middle longitudinal wall a little thinner, about If inches. With 
high pressures these walls, being flat surfaces and the valve decks 
likewise, are likely to fracture under the heavy pounding. To 
avoid making them excessively heavy they are often strongly ribbed, 
either on the inside or outside, usually the former. 

The curving side walls are of better form to withstand pres- 
sure, and need not be as thick, 1 inch being sufficient. This can 
be decreased to J inch in the suction passage below the deck, where 
little pressure exists. 

Outer Head. The outer head is also considered strong enough 
at 1 inch thickness, on account of its curved shape. It requires 
J-inch studs. Studs are preferred to tap bolts in this case, as in all 



MACHINE DRAWING 201 

other similar cases, on account of the frequent unscrewing of the 
nuts for purpose of removal. One or two unscre wings of a tap bolt 
in cast iron will destroy the tightness of the thread, while the stud, 
being steel, stands the wear better. 

Valve Seats. The valve seats are taper screwed into the deck; 
they are sometimes forced in on a plain taper fit. They are located 
as closely as strength of the deck between the holes will permit. It 
is not well to place the edge of the valve closer than \ inch from the 
cylinder walls. The valve holes in the lower deck should be in line, 
or nearly so, with the holes in the upper deck, in order to allow the 
shank of the mill to pass through when milling the lower holes. 

Miscellaneous Details. The suction opening is 7 inches in 
diameter, 12|-inch flange, lOJ-inch bolt circle, f-inch tapped 
holes. 

By means of the hand hole at the end of the suction passage, 
any dirt which may have been brought in through the suction pipe 
may be removed. 

The water cylinder cap, discharge ell and air chamber may 
be laid out from the detail Plate K, and the student must do this to 
see that the parts actually go together properly. 

With the foregoing discussion the student should be able to 
produce Plate I, which is the preliminary step to the detail drawing 
of the water cylinder as shown on Plate J. 

PLATE J. WATER CYLINDER 

Complications in Design. The water cylinder is, perhaps, the 
most complicated detail that the student will meet in this set of 
plates. Fundamentally, it is simply a box with curved sides, 
divided by the several walls into five compartments, each of which 
communicates with the outside by a round nozzle or flange. If 
this basic idea be kept constantly in mind, the student will have no 
trouble in building up the detailed design. 

This fundamental conception of a complicated piece is a very 
important idea, and should be developed carefully by the student. 
It is one of the great secrets of good design, both from an artistic 
and a commercial standpoint. We often see a machine which seems 
to begin anywhere and end nowhere; it appears to be a miscellaneous 
collection of bosses, lugs, ribs, and flanges. There is no general 



202 



MACHINE DRAWING 




MACHINE DRAWING 203 

prevailing shape to the structure, no harmony of the lines. This is 
because the designer, if he may be so called, did not have the funda- 
mental notion of shape, to which all minor details should have been 
subordinated. He simply grouped parts together, without con- 
sidering the fundamental structure. 

In this water cylinder the box is the basic part of the structure, 
and its lines must be first developed; they should be designed to 
convey a smooth, regular, and consistent surface to the eye. Then 
the nozzles and flanges may be added as subordinate parts; they will 
merely interrupt, but not destroy, the prevailing outline of the box. 
The dotted lines in the cross-section views of Plate J show the general 
shape behind and beneath the nozzles. 

The hand holes are the same as on Plate K, and the detail of the 
cover should specify the number required for both places. 

Provision for draining the four chambers of the water cylinder 
is made by the f -inch pipe tap holes at the lower deck, and the cap, 
likewise, by the single hole at the upper deck. Drip cocks are 
screwed into these holes. 

The holding-down bolts should not be less than 1 inch diameter; 
1J inch would perhaps be better; and the holes in the foot should be 
drilled at least J inch large. 

Dimensions. It will be noticed that this plate has dimension 
lines, but no figures. This is because the cylinder is rather difficult 
to figure, and it is desired to guide the student in arrangement 
of the figures without lessening the benefit of his study of them. 
Special attention should be paid to this feature of the plate. Notice 
that although space for dimensions is restricted, a clear opening is 
always found for the figures; and when one view seems to offer no 
space for a figure, another view gives the desired opportunity. 

No finish marks or titles are shown on this plate, these being 
left entirely to the student for insertion. 

Molding. The centers of the curves for the sides being on the 
main horizontal axis of the nozzles, the cylinder, if molded to be cast 
vertically as shown, will draw readily both ways from this line. 
The exceptions to this easy draw are the foot, suction nozzle and 
flange, and hand-hole boss. On account of the inside of the cylinder 
being cored, these pieces if made loose on the pattern have ample 
space to be "pulled in" after the main pattern is withdrawn. 



204 MACHINE DRAWING 

The suction passage below the deck communicates with the 
main core through the valve holes, hence it may be supported 
from the main core. This involves some difficulty, however. If 
a three-part flask be used, and another parting established at the 
center of the suction flange, in addition to the previous one, the 
problem becomes much simplified. 

It is desirable to make the four chambers of the cylinder alike 
in general proportions. It is then possible to make a single core- 
box, and by the use of loose pieces change the length of the nozzle 
cores and transpose from right to left, thus saving labor on the 
pattern. This, however, multiplies the loose pieces on the pattern. 
The many pieces are likely to become lost and make frequent repair 
necessary. Hence it is not always wise to use a single core box too 
much, and good judgment is required to fix the limit. 

Machining. Special double horizontal boring machines are 
now in common use for such cases as this, water cylinder. The 
centers are made adjustable, so that within limits any distance 
between piston-rod centers can be met. The advantages of double 
boring are, of course, most obvious for a considerable number of 
duplicate cylinders. 

It will be noticed that the face of the suction flange is carried 
out flush with the cylinder head face. This affords opportunity 
for finishing all the end surfaces at a single setting of the tool, 
whether the work be done on the rotary or reciprocating planer. 
This same point might have been observed on the small hand-hole 
boss at the other end of the cylinder, but the advantage gained 
did not seem to warrant extending the "reach'' through the hand 
hole. 

PLATE K. WATER CYLINDER CAP AND AIR CHAMBER 

Specifications. For a water cylinder cap of this size, the most 
difficult problem is to find room for the hand-hole bosses. A hand 
hole 4 inches X 6 inches is about as small as can be used, and this 
calls for a flange at least 7 inches X 9 inches. These are the pro- 
portions shown on the plate, and since the boss overhangs the bolts 
in the main-cap flange, it must be cut away underneath to clear the 
nuts. If three stud bolts are used on each side, this overhang also 
requires that the nut be "fed on"; that is, screwed on little by little 



MACHINE DRAWING 



205 



CO 


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1 

5 




u- 

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HI 

8 




cc 


X 




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10 


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206 MACHINE DRAWING 

as the end of the stud protrudes above the flange when the cap is 
being lowered into place. This is an awkward process, but it is 
sometimes necessary. 

The discharge ell should have an easy bend; usually the radius 
is somewhat more than the outside diameter of the pipe. It is 
customary on this piece to provide an opening for the attachment 
of a relief valve as shown, l|-inch pipe tap. This valve can be set 
to open at a desired pressure, so that the water end may be relieved 
in case of accidental excessive pressure. 

The air chamber provides an air cushion for the water to make 
the delivery more constant, and take the shock which would other- 
wise come with hammer-like force and full intensity upon the cyl- 
inder. Being placed at the highest point of the water end, air will 
naturally tend to collect in the air chamber and keep it charged. 
In some cases, however, a special charging device is necessary. 

Molding and Machining. The hand holes being at an angle 
will not "draw". Hence cores must be set for these openings at 
least, and it may be desirable to core out the whole inside of the cap 
for the sake of keeping the pattern in good shape by making it solid. 
Otherwise it is easy to let it leave its own core. 

The overhang of the hand-hole bosses requires loose pieces 
for the overhanging part. They are "pulled" in after the pattern 
is drawn. 

The molding and machining which are further required on 
details of Plate K are simple, and require no special discussion. 

PLATE L. PLUNGER AND VALVE DETAILS 

Specifications. Plate L is noticeable for illustrating a method 
of drawing details not used elsewhere in this set of plates. On the 
other plates each piece is separately detailed. On Plate L the details 
of the valve, cover, seat, stem, and spring are shown assembled, 
and dimensioned without separation. This is an allowable method 
when clearness is not sacrificed, but it is usually found desirable 
only with simple construction. It concentrates parts on the draw- 
ing, and probably saves some time, besides showing the workman 
just how the parts go together. The only test which the student 
need to apply in this, as in any method of detailing, is the test for 
absolute clearness. 



MACHINE DRAWING 



207 




208 MACHINE DRAWING 

It is believed in the case of the valve as shown that the details 
are completely illustrated without sacrificing clearness. Special care 
in putting in dimensions is of necessity required. 

The valve stem can be unscrewed either with a socket wrench 
on the inside or an ordinary fork wrench on the outside. 

The seat, after being screwed to position in the deck, is often 
faced off, to true up any distortion caused by screwing in. 

The valve itself, of rubber, can be bought of any desired grade 
of hardness. The specification for any given set of valves depends 
upon the quality of the water, the pressure, and the general service 
of the pump. 

Molding and Machining. By reason of the simple nature of 
the parts on this plate, the molding and machining is left entirely to 
the original consideration of the student. 

PLATE M. FOUNDATION 

Specifications. Pumps are often set directly upon a foundation 
of brick, but it makes a better job to bed stones, with surfaces 
dressed plane and true, into the main foundation, and rest the pump 
feet upon these stones. The simplest form of holding down bolts is 
shown on Plate M, a plain hook at the lower end, pulling up against 
a flat cast-iron plate, to distribute the pressure into the brickwork. 
These plates are of course bedded, and the bolts set as the founda- 
tion is built up. As the subsequent courses are laid some little 
space is left around the bolts, which may be afterwards filled with 
cement, thus making the bolts rigid with the foundation. 

The water end of the foundation has no batter, because the 
suction pipe often drops vertically down from the end of the pump, 
and clearness is therefore necessary. 

The floor line is placed 4 inches above the brickwork, to allow 
for the usual 1-inch top floor and 2-inch plank beneath, and still 
have a space left for shims to level the floor. 

PLATE N. GENERAL DRAWING 

Assembled Parts. Plate N is an example of a plain, everyday 
shop drawing, to show the relation of parts and the extreme space 
occupied by the pump. A great deal of time can be needlessly 
wasted in producing a drawing of this character, by trying to make 
too faithful a picture. For example: If all the bolt heads were 



MACHINE DRAWING 



209 




MACHINE DRAWING 211 

put in, it is safe to say that several hours 5 extra time would be 
required for this one item alone. But the drawing would be no 
better for shop use. Hence all bolt heads and nuts have been left 
out, except when necessary to show clearance. 

An assembly or general drawing of this character should be 
laid out strictly from the dimensions shown by the details. It 
thus serves a valuable purpose in checking up figures, and showing 
whether or not the parts will go together. The method or char- 
acter of the work in no respect differs from that suggested for the 
detail drawings. 

If a scale of 3 inches = 1 foot be used, the size of sheet must 
be 24 inches X 36 inches. The student, however, will perhaps find 
it easier to use a scale of 1J inches = 1 foot, in which case the ordi- 
nary size, 18 inches X 24 inches, will suffice. For such a small scale 
it will be found undesirable to attempt to put in any very small 
fillets and corners, although those that can be readily handled by 
the ordinary bow pen ought not to be omitted. As a matter of fact, 
the expert draftsman either leaves the corners sharp, as suggested, 
or puts in the smallest curves freehand. 

Order Sheets. Any set of drawings is incomplete unless in 
connection with it a statement is made in tabular form of the com- 
plete make-up of the machine. An infinite variety of ways exists 
for making the specifications. Sometimes the tabulated data are 
placed on the general drawing. Most often, however, printed blanks 
are provided, usually of bond paper, arranged with special reference 
to the individual shop system and methods of handling work; these 
blanks are filled in by the draftsman, indexed, and filed as a part of 
the set of drawings. They can be blue-printed for use in the shops 
the same as a drawing. From these sheets stock is ordered, checked 
off, and watched in its process of manufacture. 

Order sheets are indispensable in any well-ordered shop. Hence 
they are illustrated in the pages following the text matter as the 
final step in the set of pump drawings. They are made as simple as 
possible, and are not intended to fit any special shop system. As 
previously stated, the exact form and method of classification can 
be determined only when the shop conditions are known. 

The student, having carefully followed through the preceding 
pages, must not think that he is master of pump construction, for 



212 MACHINE DRAWING 

even the type illustrated has been but touched upon. The object 
of the detailed discussion is to get the student in close touch with 
the spirit of construction, to make his drawings real, serious work. 
It is hoped that the student will work just as though a machine 
were to be built from his drawings, and built to sell at a profit. Only 
in this way can advanced work in mechanical drawing be of benefit 
to him, for after becoming expert in the use of the instruments, no 
other advance is possible except advance in thought. 



MACHINE DRAWING 



213 



date. american school of correspondence type, 
oct. 10, 1913. inside plunger. 

Chicago, III. 
LIST OF CASTINGS 

FOR 

16— 8i— 12 DUPLEX PUMP. 


a 
6 


Name. 


6 

a 
% 

c3 
u 

p 




is 

s 

-►J 

3 


Remarks. 


2 


Steam Cylinder 


B 




C.I 




R. h L. 


2 
2 


Steam Cylinder Head 


B 




C.I 






bteam Chest 


D 




C.I 






2 


Steam-Chest Cover 


D 




C.I 






2 


Slide Valve 


D 




C.I 






1 


Steam Pipe 


D 




C.I 






1 


Exhaust lee 


D 




C.I 






2 


Valve Stem Gland 


D 




C. 1 






2 


Piston 


C 




C.I 






8 


Piston Pipe Plug, \\" 


C 




C.I 






4 


Piston Packing Ring 


C 




C.I 






2 


Spool 


C 




0. 1 






1 


Steam Cylinder Cricket 


H 




C.I 






2 


Steam Cylinder Stuffing Box 


H 




C.I 






2 


Water Cylinder Stuffing Box 


H 




C.I 






4 


Piston-Rod Gland 


H 




C.I 






1 


Valve-Lever Bracket 


H 




C. I 






2 


Yoke 


H 




C. I 




R.&L. 


1 


Short Rocker Arm* 


G 




C.I 






1 


Long Rocker Arm 


G 




C.I 






2 


Valve Stem Link 


G 




C.I 






1 


Water Cylinder 


J 




C.I 






2 


Water Cylinder Head 


J 




C.I 






3 


Hand Hole Cover 


J 




C.I 






1 


Water Cylinder Cap 


K 




C. I 






1 


Air Chamber 


K 




C.I 






1 


Discharge Ell 


K 




C.I 






2 


Plunger 


L 




C.I 






2 


Plunger Bushing 


L 




Brass 




2 


Clamp Ring 


L 




C.I. 




32 


Valve Stem 


L 




Brass 




32 


Valve Cover 


L 




Brass 




32 


Valve Seat 


L 




Brass 




6 


Foundation Plate 


M 




C.I. 





214 



MACHINE DRAWING 



date. american school of correspondence type, 
oct. 10, 1913. inside plunger. 

Chicago, III. 
LIST OF STEEL AND MISCELLANEOUS PARTS 




FOR 

16—81—12 DUPLEX PUMP. 


-d 

a 

d 


Name. 


d 
ft 
bO 

a 
'$ 

u 

Q 


d 

3.8 
P4P4 


[3 


Remarks 


2 


Valve Steam Head 


C 




St. 


Drop Forging. 


2 


Piston Rod 


c 




C. R. S. 




2 


Valve Stem 


c 




St. 




1 


Long P. R. Lever 


G 




St. 


Forging 


1 


Short P. R. Lever 


G 




St. 


Forging 


1 


Upper Rocker Shaft 


G 




St. 




1 


Lower Rocker Shaft 


G 




St. 




2 


Rocker Arm Pin 


G 




St. 




2 


Link Pin 


G 




St. 




1 


Long P. R. Lever Key 


G 




St. 


Drop Forging 


1 


Short P. R. Lever Key 


G 




St. 


Drop Forging 


2 


Rocker Arm Key 


G 




St. 


Drop Forging 


32 


Valve Spring 


L 




Bs. wire 


Spring Temper 


32 


Valve 


L 




Rubber 


Medium 







































MACHINE DRAWING 



215 



date. American School of Correspondence type, 
oct. 10,1913 • inside plunger. 




Chicago, III. 
LIST OF BOLTS, NUTS, AND PINS. 


FOR 

16—81—12 DUPLEX PUMP. 










T3 
(0 

a 
6 


Name. 


d 

M 

a 
'$ 

Gj 
U 

Q 


d 

• o 


13 
2 


Remarks. 


24 


Cylinder Head Stud f x 3£ 


B 




St. 




20 


Steam Chest Stud f x 8f 


B 




St. 




4 


Valve Stem Gland Stud f x 4| 


D 




St. 




8 


Piston-Rod Gland Stud f x 4 


H 




St. 




24 


Water Cylinder Head Stud | x 3| 


J 




St. 




12 


Clamp Ring Stud f x k\ 


J 




Tobin bz 




24 


Water Cylinder Cap Stud 1x3^ 


J 




St. 




18 


Hand Hole Cover Stud f x 2\ 


J 




St. 




12 


Hand Hole Cover Stud f x 2\ 


K 




St. 




8 


Exhaust Tee Tap Bolt f x If 


B 




St. 




16 


Yoke Tap Bolt f x 2 


B 




St. 




8 


Steam Cyl. Stf . Box Tap Bolt f x If 


B 




St. 




8 


Steam Pipe Tap Bolt f x If 


D 




St. 




4 


Valve-Lever Bracket Tap Bolt f x If 


D 




St. 




4 


Steam Cyl. Cricket Tap Bolt 1 x 2| 


D 




St. 




16 


Yoke Tap Bolt f x 2 


J 




St. 




8 


Water Cyl. Stf. Box Tap Bolt f x If 


J 




St. 




8 


Discharge Ell Tap Bolt f x 2 


K 




St. 




4 


Air Chamber Tap Bolt f x 2 


K 




St. 




2 


Hook Bolt (special) 1x3' —11" 


M 




St. 




4 


Hook Bolt (special) \\ x 3' — 11" 


M 




St. 




1 


Eye Bolt Standard 1" 


K 




St. 




34 


Standard Nut f 






St. 




44 


Standard Nut f 






St. 




36 


Standard Nut f 






St. 




26 


Standard Nut 1 






St. 




4 


Standard Nut \\ 






St. 




4 


Standard Nut 2 






St. 




8 


Special Valve Stem Nut 1 






St. 


| Thick 


4 


Piston-Rod Split Pin \ x 2 


1 c 




St. 




2 


Spool Taper Pin No. 10 Morse Taper 


c 




St. 


4" long 


4 


Valve Bracket Dowel Pin \ x 2 


H 




St. 





216 



MACHINE DRAWING 



date. American School o f Correspondence type, 
oct. 10, 1913. inside plunger. 

Chicago, III. 
LIST OF SPECIAL FITTINGS, WRENCHES, ETC. 




FOR 

16—81—11 DUPLEX PUMP. 


H3 

o> 

a 
6 


Name. 


d 

tD 

a 

'% 

t-. 

Q 


Patt. or 
Piece No. 


3 

V 


Remarks. 


4 


Drip Cock |" 


B 








1 


Drip Cock 1" 


D 








2 


Drip Cock \" 


H 








4 


Oil Cup |" 


H 








5 


Drip Cock f" 


J 








1 


Relief Valve \\" 


B 






175 lbs. pressure 
















Standard Fork Wrench f" 












Standard Fork Wrench f " 












Standard Fork Wrench f " 












Standard Fork Wrench 1" 












Socket Wrench f " 








12" handle 




Valve Stem Fork Wrench 













Valve Stem Socket Wrench 

































MACHINE DRAWING 217 

PLATES 

The plates of Machine Drawing Part III (A to N, inclusive,) are 
so arranged and described that the complete set may be made by 
the student. In case of insufficient time, the following short exam- 
ination is prescribed. The student in any case should read care- 
fully all the text, and follow the discussion of all the plates, whether 
or not actually produced by him. 

PLATE XI 

Make steam end layout, Plate A (page 164). This is to be done 
accurately in pencil. 

PLATE XII 

Make drawing of steam cylinder, Plate B (page 172), complete, 
with finish marks and dimensions. Do not put on shade lines. 

PLATE XIII 

Reproduce Plate C (page 185), putting on shade lines. 

PLATE XIV 

Draw valve motion layout, Plate E (page 190). This plate also 
is to be done accurately in pencil. 

PLATE XV 

Make rough freehand sketches in pencil of parts on Plate H 
(page 196), putting on finish marks and dimensions. Use a medium 
pencil, and make sheet of regular size (18 inches X 24 inches). 
Arrangement to be similar to Plate H. Do not try to make the 
sketches to scale, but make them sufficiently complete so that detail 
drawings can be made from them. 

PLATE XVI 

Make a tracing on tracing cloth of Plate C (page 185). 

PLATE XVII 

Make general drawing Plate N (page 210). Use scale of 1J 
inches = 1 foot, or 3 inches = 1 foot. 

PLATE XVIII (Optional) 

Make drawing of water cylinder, Plate J (page 202). 



218 MACHINE DRAWING 

EXAMINATION PLATES 

Plates XI to XVIII inclusive constitute the Examination for 
this Instruction Paper. The student should draw these plates and 
send them to the School for correction and criticism. The plates 
should be 18 inches X 24 inches, except in the case of Plate XVII; this 
plate may be 18 inches X 24 inches or 24 inches X 36 inches, depend- 
ing upon the scale chosen by the student. 

Plates XII and XIV are to be in pencil. Plate XVI is to be 
inked on tracing cloth. The others should be inked. 

The date, and the student's name and address, should be placed 
in the lower right-hand corner of the plate, as shown. The plate 
number should be placed at the upper right-hand corner, as in 
previous plates, the letters to be ^2 inch high. 




AUXILIARY POLE GENERATOR OF 550-VOLT AND 1500-KILOWATT CAPACITY 
INSTALLED FOR ARMOUR AND COMPANY, CHICAGO 

Courtesy of Crocker-Wheeler Company 



MACHINE DRAWING 

PART III B— ELECTRICAL 



INTRODUCTION 



Requirements. Having learned the general principles involved 
in making a correct mechanical drawing of any part of a machine, 
or the machine as a whole, it might be assumed that the student 
was in a position to work up complete shop drawings of any piece 
of apparatus when given the necessary data. However, this is 
hardly the case. The previous work took up the subject from the 
standpoint of proper portrayal, the proper way to represent a given 
object in the form of a drawing, without emphasizing the use to 
which it is to be put. 

While it is absolutely necessary that the draftsman have a 
thorough knowledge of the theory and practice of line drawings, 
it is also essential that he go farther and attain as well a complete 
understanding of the uses to which the drawings are to be put. 
He must look at the whole drawing or set of drawings as a means 
to an end, the building of the machine or piece of apparatus. 

Necessity of Thorough Groundwork. We cannot emphasize 
too strongly the necessity for a thorough grasp of the work done 
heretofore. One cannot hope to attain proficiency in machine 
drawing unless one has previously learned to make line drawings 
accurately and correctly. It is not a question of having the neces- 
sary information available in the form of books or instructions, 
but of having the information in one's mind, and the ability to 
produce the drawing at one's finger tips. The principles set forth 
in the previous works and the elementary training secured in the 
thorough mastery and study of those principles will alone form 
the proper foundation for the following work and help to produce 
an efficient draftsman. 

A Drawing Must be a Form of Instruction. The making of 
drawings will now be taken up from the standpoint of their practical 



220 MACHINE DRAWING 

use in the shop for the production of a complete machine. We 
must look at the drawing no longer as a "picture' ' but as a practical 
form of instruction to the pattern maker, to the foundryman, 
to the machinist, or to the assembler. Our object is no longer 
to show the machine or the part, but to give to the shopman such 
information that he may build the machine. 

Variations from the theoretical principles heretofore set forth 
will be found in plenty, but every variation will have its practical 
reason. Only a small part of the whole of a piece may be shown, 
when that small part tells the whole story to the shopman. The 
proper laws of projection may not be followed or the crosshatching 
may be omitted entirely from a cross section, but these liberties will 
be taken by the draftsman only that the drawing may be more clear. 

It should not be. assumed because of the above statements 
that a knowledge of the essential principles will not help in the 
making of practical drawings. The truth is quite the contrary. 
Unless one knows the principles from the beginning to the end he 
dare not take liberties for fear these liberties will confuse instead 
of clarify the work. 

Essentials of a Good Drawing. As stated in one of the earlier 
books on this subject,* the two chief essentials of a shop drawing 
are: 

(1) Absolutely complete and definite instructions from designer 

to workman. 

(2) Least possible cost in dollars and cents of production of 

the drawing measured by the draftsman's time. 

Complete Instructions, Of the above the first is the easier 
to determine, once the drawing is in the shop and in the hands of 
the workman. The least question as to form or dimension stamps 
the drawing as bad and the draftsman as a poor workman. This 
does not mean that a drawing must be a mass of lines and dimen- 
sions nor that everything must be shown on each drawing; in fact, 
the confusion which would result from such drawings would be 
as bad as the uncertainty caused by incomplete work. The exact 
shape and every necessary dimension must be shown, but no 
unnecessary line must be drawn to hinder and confuse the workman. 



*Charlea L. Griffin, Machine Drawing, Part III A, 



MACHINE DRAWING 221 

In this connection, it is well to state that many manufacturers 
prefer that much of the information be given in the form of notes 
or tables, if it will help to eliminate confusing lines or dimensions 
on the drawings. Such practices vary widely in different shops, 
and no definite rules can be laid down. 

Cost of Drawings. As to the second point — the cost of the 
drawing — it is harder to tell when "cheapness" is a real economy. 
The first point is so firmly fixed as a part of the second that for the 
cost you must always consider the two together. If a perfect 
shop drawing can be made cheaply, that is real economy. To make 
a poor shop drawing cheaply is the greatest extravagance. A 
draftsman may produce a fairly good shop drawing but may reach 
this end by unsystematic and haphazard work; the result is high 
cost of the drawing and at best only fair results. Another drafts- 
man may, although apparently working at a slower rate, reach 
the same end by careful and systematic work in less time. The 
drawings of the second man will be cheaper, and the chances are 
that his care and systematic procedure will in time assure the pro- 
duction of better and better work. 

System is essential to cheap drawings. No draftsman can 
hope to start his work in a careless and haphazard manner and 
complete it in a reasonable time or even be sure that it is complete 
when it seems to be. A definite start, a definite system of building 
up the drawing from that start, and a definite end in view will 
go far toward teaching the draftsman to produce good drawings 
at the minimum expense. 

With the above points constantly in mind, we can proceed 
to a demonstration of how a set of shop drawings are produced. 
In order to get the most good from this demonstration, much of 
it must be worked out in detail by the student himself. It is to be 
hoped that this work will go far toward instilling in his mind the 
principles involved and the necessity for constant thought, close 
application, and hard work. 

The theoretical considerations involved in the design of a 
direct-current generator, are beyond the scope of this work, but 
the production of shop drawings of such a machine, once the 
designing engineer has supplied the data, will make an excellent 
study. 



222 MACHINE DRAWING 

DESIGN OF A DIRECT=CURRENT GENERATOR 

General Specifications. The set of plates* which will be used 
presents complete drawings for a multipole direct-current gener- 
ator having six main poles and commutating poles, running at a 
speed of 600 revolutions per minute, and rated 250 volts 300 kilo- 
watts. This rating must be abbreviated on the drawings, the 
manufacturer having a definite form which is always followed, thus : 
M. P. C. 6-300-600-L-250 V. M. P. means multipolar; C means com- 
mutating field; L means the form; and the figures indicate number 
of poles, kilowatt output, speed, and voltage, respectively. This 
tells all that is necessary regarding the rating of the machine. 
Form letters may sometimes be added to indicate some special 
features of design, but these are peculiar to the manufacturer. 

Material Supplied to Designing Draftsman. In any electric 
machine, the design must be an intermingling of electrical and 
mechanical features. The designing engineer usually gives more 
of the mechanical details than in some other classes of machinery 
because these details affect the electrical features. Practice varies 
in every manufacturing plant to some extent in this respect. Thus, 
in one place the engineer may go so far as to determine the size 
of the shaft necessary, while in another the calculation of some of 
the electrical features may be left to the designing draftsman. 

In general, the designing draftsman is supplied with complete 
tables of the electrical features giving all details of the various 
windings, the length or size of the magnetic circuits, and the mate- 
rial to be used for them, together with any other features of design 
which must be followed in order to meet the requirements. The 
electrical features may be given in the form of tables which may 
give all necessary data as to size and number of conductors in fields 
and armature, the size and arrangement of slots in the armature 
laminations, and the kind of insulation and its arrangement. From 
this data the draftsman must make his drawings complete in every 
detail, so that the machine can be built in the shops. The informa- 
tion contained in the drawings must be such that every workman, 
from the pattern maker to the assembler, can do his work without 
other help. 

♦Courtesy of the General Electric Company, Schenectady, N. Y, 



224 MACHINE DRAWING 

PRELIMINARY LAYOUT SKETCH 

Pencil Sketch. The designing draftsman may make first 
a sketch or preliminary drawing showing the outline of the machine, 
with such dimensions as may be determined from the designer's data. 

PLATE A. GENERAL OUTLINE DRAWING 

Plate A shows such a preliminary outline drawing. It will 
be seen that this drawing is more or less rough. There is no detail 
and there are no dimensions except such as are determined by the 
designer's data and the known requirements as to over-all dimen- 
sions, such as length from face of coupling to end of outboard bearing, 
height from floor to center line of shaft, etc. No pains have 
been taken to make the drawing of value to the shopman, since 
it is used only in the drafting room. It gives the detail man a 
better idea of the whole machine than the data submitted by the 
designer. While the lines are put in without much regard to detail 
or accuracy, they convey the proper idea, and time spent in 
unessentials would be wasted on such a drawing. 

Value of Layout Drawing. The draftsman now has, in addi- 
tion to the designing data, a sketch giving information to the eye 
as well as to the mind. He sees at once that a start must be made 
from this and, if he is a good draftsman, he knows that he must 
as far as possible work out completely each part as it is reached. 
He should avoid starting any part unless enough is already known 
to finish that part. This principle cannot always be followed, 
since some parts are interdependent and must be worked up to- 
gether before they can be detailed individually. 

DETAILS OF ARMATURE AND COMMUTATOR 

In the case in hand, it might seem the logical thing to start 
with the center of the machine — the shaft — and work outward, 
completing each part as it is reached. However, if we start with 
the shaft, we soon find that we do not have sufficient data to com- 
plete the drawing. While the designer has given some data from 
which we could start, as for instance the length between bearings 
and the weight, we must also know the dimensions of the armature 
and commutator spiders before the shaft drawing can be completed; 
therefore, we must first work up the armature and commutator. 



MACHINE DRAWING 



225 




226 MACHINE DRAWING 

PLATE B. ARMATURE PUNCHINGS 

The armature laminations, Fig. 1, can very easily be drawn, 
since the designer has given all the necessary data as to dimensions, 
and it is only necessary for the draftsman to put this data on a 
drawing for the use of the shopman. 

Details of Slots. It will be noted that the slots are very care- 
fully detailed, Fig. 3, the dimensions in all cases being given in 
decimals and figured to several decimal places, depending upon the 
accuracy necessary. The actual dimensions of the piece and the 
slots are taken from the engineer's design data. 

Assembly of Punchings. The punchings are assembled as 
shown in Fig. 2 of this plate to give over-all dimensions as shown; 
that is, the number of pieces is determined in assembling only by 
the total thickness required. A J"Xft" keyway is provided, the 
use of which will be understood when the spider is drawn. The 
space blocks are inserted at intervals in order that openings may 
be left through the armature for ventilation. These space blocks 
are not detailed on this drawing and consist merely of metal pieces 
which, it will be noted, are riveted to two laminations, so that 
they are held rigidly in place. 

PLATE C. ARMATURE WINDINGS 

Layout of Winding. It will next be necessary to lay out 
the armature windings themselves in order that we may complete 
the details of the flanges and spider. Note now how the drafts- 
man has made a diagram, Fig. 7, showing with single lines how the 
conductors are to be arranged. He has taken the first and nine- 
teenth slots, showing the conductors as lines; he has shown the 
first three and the last commutator bars, to show their relation 
to the conductors; and finally, he has made an end view, showing 
the relation of the conductors in the slots. 

Detail Drawing of Coils. He next draws the same set of 
coils to such a scale as will show all necessary detail, Figs. 1, 2, 3, 
and 4, putting on full and complete dimensions as obtained from 
the design data and the dimensions of the armature core, and as 
determined from the coils themselves. 

Cross Section of Coil in Slot. A cross section of one set of 
conductors in one slot is next drawn, Fig. 5. This must necessarily 



228 MACHINE DRAWING 

be drawn to a very large scale, such as twice the size, in order that 
all dimensions may be shown without sacrificing clearness. In 
this section it should be noted that several diametrical dimensions 
are given and that the dimensions of the slot are shown along with 
the corresponding dimensions of the coil. 

Side View of Assembly in Armature Core. A side view of 
the coil assembled in the armature core is next shown, Fig. 8. This 
view shows a number of details which are covered completely with 
very little labor. For instance, the binding wires are shown and 
described completely, although nothing more than a section is drawn. 
This illustrates very well the use of good explanatory notes and 
their value as labor savers. This view also shows the armature 
flanges and determines their general dimensions, as related to the 
coils. 

Another point in connection with this drawing which should 
be given attention is the method of calling for the various parts. 
It will be noted that a table is included in the lower right hand 
corner. This table gives on the right the name of each part, with a 
number which refers to a corresponding number in the body of 
the drawing. Note that these numbers on the drawing are made 
large and enclosed in circles, and that arrows are added where 
necessary to call attention to the proper part. The table contains, 
still farther to the left, the proper material to be used and the number 
of parts required. Such tables are used by some drafting rooms 
and undoubtedly prevent confusion due to placing too much data 
on the body of the drawing. 

Another point should be noted. The drawing is made pri- 
marily to show the armature coils, and to do this we have a plan, 
a side elevation, and a section. The plan and elevation do not 
bear the relation on the sheet that the laws of projection require, 
but nothing in clearness is sacrificed, space is saved, and the drawing 
is really made easier to read. 

In addition to showing all necessary details of the coils, suf- 
ficient data is given from which to make the next drawing. In 
other words, we have determined enough of the physical dimensions 
of the armature flanges to know how they must be built to support 
properly the ends of the coils, giving necessary clearances for insu- 
lation, etc. 



230 MACHINE DRAWING 

PLATE D. ARMATURE FLANGES AND SPIDER 

We come logically then to the armature flanges and the spider. 

Difference Between Front and Back Flanges. The two flanges 
are quite similar in everything except as regards their mounting 
on the spider. The one for the back end of the armature, Fig. 2, 
merely slips back over the arms of the spider against a shoulder. 
The laminations are placed on the spider, and then the front flange, 
Fig. 1, must be arranged to press the laminations against the back 
one, and must be held solidly in place. Note that the inside diam- 
eter of the back flange is given in decimals to a thousandth of an 
inch and marked spider fit. Now note the corresponding dimen- 
sion on the front flange. While the dimension is an even eighteen 
and one-half inches it is given to three decimals, indicating that 
the machining must be done so that the given dimension is within 
one thousandth of an inch. This shows the workman at once 
where the fine work is to be done and, compared with other dimen- 
sions, shows the relative care which must be taken to make the 
size as shown. 

This drawing also shows, very clearly, how a whole piece may 
be covered in the drawing by showing only a part. Nothing what- 
ever could be added to the drawing by showing the whole of these 
two flanges, while more space would be required and more time 
would be needed to draw it. 

It will be noted that the sections are identified on the plans 
by lines drawn across them at the points where the sections are 
taken, these lines being lettered, and a note added below the section 
giving the proper reference. 

Finish Notes for Shopman. Another thing should be noted 
as showing how the draftsman must consider the pattern maker. 
The pattern maker must make proper allowance for shrinkage 
and for machining, and wherever a part is marked "finish" by means 
of the usual /, he will add to the dimensions shown in making his 
pattern. Now note the arms of these flanges, shown in section on 
Figs. 1 and 2. Instead of putting the / across the surface to be 
finished, a note is given which tells the pattern maker that, while 
it is to be rough finished, no extra allowance is necessary. 

This simply illustrates the original point of the whole matter; 
the drawings are for the shopman, and every point, no matter how 



MACHINE DRAWING 231 

small, must be covered so that there can be no doubt in his mind 
as to how to proceed. 

Armature Spider Details. Now, taking up the spider, Fig. 3, 
it will be seen that the outside dimensions are determined by those 
of the flanges. The shaft diameter must now be calculated, if 
not given by the designer, and we can proceed to complete this 
drawing. 

Note how the center of the spider is cored out to save metal, 
how fit dimensions are carefully marked in and given in decimals 
where close work is desired. Note the keyways for laminations, 
front flange, and shaft, and note how the keys are called for in 
the table in the corner. 

Another point of interest is the way in which the draftsman 
has shown a section through one arm of the spider but has shown 
the other one full. By "bending" the section line A B C he has 
added clearness to the drawing and saved crosshatching consider- 
able space. As to this crosshatching, many drawing rooms save 
time by the method shown here. Instead of making the usual 
parallel lines, the space is filled in with a pencil, giving a clouded 
appearance when blue-printed. 

On the left end of the spider are shown the shoulder and tapped 
holes for the equalizer support. The equalizer support cannot 
be drawn until the equalizer rings have been laid out and the 
dimensions determined (See Plate E). 

PLATE E. EQUALIZER RINGS AND SUPPORT 

General Details. The equalizer rings just referred to may 
now be designed. First a diagram is drawn showing the general 
shape and the points at which they are connected into the risers, 
Fig. 5. The details are next worked up, showing the exact form 
and all dimensions, Fig. 1. A note giving insulation data is added, 
the thickness being given as usual in mils or thousandths of an inch. 

Assembly Drawing. From the above an assembly is devel- 
oped, Fig. 6, showing the rings in place under the armature coils 
and supported by a ring attached to the armature spider. As in 
the case of the armature coils, the binding wires are shown and 
notes included giving number of turns, size of wire, stress on the 
bands, and tension on the wires. 



232 



MACHINE DRAWING 




Insulate with 2 layers 
of varnished cambric 
covered with bre 
/men drill. 



Stress on bands - 18 IS lbs. 
Tension on P.B. Wire. 340 to 380 lbs. 




Note Bars to be insu 
of S mil cotton tape 




ated with 2 /auers 
£ach layer half 



Zapped and varnished to 14 mrfs 



Peve-foped lenofh aporox.26g+jf 
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MACHINE DRAWING 233 

Equalizer Ring Support. From the data already given in 
Fig. 6 and on Plate D, the support for the equalizer rings may now 
be drawn, Fig. 7. The principal dimensions are determined from 
the previous drawings and it only remains to work out the details, 
which need no explanation. 

PLATE F. COMMUTATOR DETAILS 
Commutator Drawing Requires Special Care. Now we come 
to the commutator, clamping rings, and spider or shell. Plate F 
is a splendid example of detail work where the draftsman must 
work out dimensions to the finest point, considering only not the 
foundry man, the machinist, and the assembler, but the ultimate 
result to be obtained and the use to which this part of the machine 
is to be put. Here we have a device which must consist of 216 
copper bars insulated from each other, from the supporting shell, 
and from the clamping rings, having a given length and wearing 
depth and assembled in a cylinder having a diameter of about 
23 inches. It is obvious that the only way these bars can be held 
in place is by clamping rings drawn up against beveled surfaces 
on the ends of the bars,' with proper insulation between the indi- 
vidual bars and between the bars and the rings. Insulation must 
also be placed between the bars and the shell. 

Dimensions of Commutator Sections. It will be seen that 
the dimensions can only be expressed in decimals, if accurate re- 
sults are to be obtained. Note now the width of the top of each 
bar — .2963 inch shown in Fig. 5 — and, taking this dimension 
and the insulation thickness between each bar of .0382 inch, 
check back and find the circumferential length. Now compare 
this figure with the circumference of a circle whose diameter is 
23 inches. It will be found that the thickness of the bars has been 
figured so closely that the total error in the length of the circum- 
ference will only be a matter of thousandths of an inch in a total 
length of some six feet. Such work is only possible by means of 
very fine gages. A reference will be found to a gage number, which 
means that the tool maker must make a gage accurate within one 
ten-thousandth of an inch, which will be used by the workman 
in making these bars. 

It should be noted that all dimensions between concentric 
surfaces are referred to radial or diametrical distances. This 



234 



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MACHINE DRAWING 235 

certainly shows that the draftsman understood his business. The 
"whole construction is such that diameters or radii are the fixed 
dimensions, and any attempt to give these dimensions in any other 
way would cause the shopman to calculate the diameters with 
great chance for error. 

Complete Information for Shopman. It might be well at 
this point to emphasize the importance of giving information on 
the drawing in such a way and in such completeness that the shop 
man need ask no questions; in fact, modern shop practice requires 
that the workman work entirely from the drawing and the dimen- 
sions given there, and under no circumstances is it permitted the 
shopman to make any calculations. It should also be remembered 
that it costs much more to make additions to or changes on a drawing 
than the same work would have cost, if done when the drawing 
was made in the first place. And so we see that even so small a 
thing as one of these commutator bars is given closest attention, 
and each detail is worked out so that when the whole thing reaches 
the assembler it will be as easy to put together as if it were two 
pieces instead of several hundred. 

Assembly Drawing. This plate is another good example of 
how the draftsman may completely describe the whole by showing 
only a part. The assembled view, Fig. 1, loses nothing by showing 
a section of less than half the commutator; in fact, to spend time 
and money showing more would certainly be wasteful. The same 
may be said of the other parts shown on this plate. 

The assembly shown gives the general scheme of placing the 
parts of the commutator together so as to perform the proper func- 
tions. From this, the other details can be developed. 

Details of Armature Shell. First we must have a shell for 
supporting the bars and rings. This can be made in the form of 
two concentric cylinders with supporting arms between, Fig. 2. 
The size of the shaft has already been decided upon, so we can 
start with this dimension. It is not desirable to make this piece 
fit the shaft throughout its entire length since it would require 
a difficult job of boring in the shop and would add nothing to the 
finished piece. The casting is therefore cored out by the foundry 
man, so that there will be two bearing surfaces each 4J inches long 
to be bored, but the central portion of the hub need not be finished. 



236 MACHINE DRAWING 

This saves considerable time in the machine work. The thick- 
ness of the hub is only enough for mechanical strength to carry 
the commutator. The same is true of the arms and outer shell. 
In other words, as little material is used as possible to give the 
desired strength, with a proper factor of safety. Thus we have 
the arms 1 inch thick and, of course, the full length of the shell. 
The outer shell, having a number of holes through it for the studs 
for drawing up the rings, must be somewhat thicker than the hub. 
Also the rings must be considered and these holes spaced so that 
they will not come too close to the inner edge. The various holes, 
being rather hard to show clearly, are described in notes at one 
side of the drawing. These notes give size of hole, threading data 
when necessary, and any other information as to number, loca- 
tion, or depth that may be required. 

It should be noted that those dimensions which must be 
machined very closely are given, as in other plates, to three and 
four decimal places. The usual notes and marks as to finish and 
fits are included. 

Clamp Rings. The clamp rings, Figs. 3 and 4, are fairly 
simple as to form, but accurate and careful work is shown in making 
the drawings, and the information must be quite as clear and 
complete as for the more complicated-looking pieces. Note how 
many dimensions are given and the reasons for them — for instance, 
the angles of the cone faces which must check with the cor- 
responding angle on the commutator bars, and the radius of the 
curve between the cone face and the vertical face which must be 
such as to turn the insulating cone without any tendency to break 
it. Since these rings are finished all over, a single note to that 
effect saves the time of putting the usual marks on all finished sur- 
faces. 

Surely the shopman will have little trouble in building this 
commutator from the drawing, with its wealth of detail information. 
How many dimensions could be omitted and how many lines left 
out and still be sure of the information being complete? Just 
enough is shown, just the right number of dimensions are given, 
to give complete instructions to the shopman at the smallest pos- 
sible expense. This stands for efficiency in drawing and in building 
from the drawings. 



238 MACHINE DRAWING 

PLATE G. ARMATURE SHAFT 

Details and Dimensions. The revolving parts have now 
been completed with the exception of the shaft. From the previous 
drawings all data is available for making the shaft drawing as shown 
in Plate G. The center lines of bearings, the center line of the 
armature, and the center line of the shaft itself will give the start- 
ing points. The size of the main section of the shaft and of the 
bearings has been determined. Note that the bearing at the coup- 
ling end is larger than the other one since the strains there are 
greater. The total length of bearing between oil deflectors is made 
slightly greater than the length of bearing to allow for end play 
of the armature when running. 

Oil Rings. If the shaft were extended in smooth lines toward 
the center, the oil would gradually creep along the shaft until it 
reached the spider or commutator shell where it would be thrown 
out into the machine. Rings are therefore formed on the shaft 
which will throw off the oil inside the bearing housing. These 
deflectors are shown on a larger scale so that the details can be 
given more clearly. Sections through the shaft for the purpose 
of showing the key ways are also given. Note how the finish is 
given according to whether it is for a fit with some other part or 
is a polished journal finish. 

Couplings. The coupling is also shown on this plate, since 
it forms a part of the shaft. The dimensions are given in decimals 
where they affect the other half coupling which will be furnished 
by the manufacturer of the prime mover to which the machine is 
to be coupled. 

The keys are called for in the title table by dimensions, no 
other information being necessary. 

It will be noted that only enough of the sections of armature 
spider and commutator shell are shown to give their location on 
the shaft and furnish needed dimensions. 



DETAILS OF FIELD FRAME AND COILS 

Having completed the revolving member, we now turn our 
attention to the magnet frame, fields, etc. 



240 MACHINE DRAWING 

PLATE H. MAGNET FRAME AND BASE 

General Details. The details of the magnet frame are covered 
by Plate H. Certain dimensions here are fixed by the electrical 
design in order to give the proper amount of iron in the frame, 
the proper size field cores, and proper spacing of fields. The frame 
is made split horizontally at the center line, and the two parts are 
symmetrical, except that the lower half must have proper feet 
at the points where it rests on the base. Only one of the lower 
quarters, Figs. 1 and 2, is shown in the drawing, since this will give 
all necessary dimensions and instructions for the entire frame and 
the lower half is symmetrical about a vertical center line. 

Arrangements for Bolting Frame and Pole Pieces. The work 
on this drawing consists mostly of locating and dimensioning the 
parts already fixed by the designer and completing the mechanical 
details. There are some very interesting things to be seen in con- 
nection with some of these mechanical details. There is a pole 
on each side of the machine which must come exactly at the split, 
Fig. 2. The holes for the bolts which hold these pole pieces must 
come at a point which will clear the studs holding the two halves 
of the frame together. Also two of the poles come where the feet 
are located. It will be seen that the casting is made hollow at 
this point (see sketch marked Section "DD") and the bolts for 
these poles are put through from this space. The studs for holding 
the two halves of the frame together also come down into this space. 
A steel cover plate is provided so that the rough casting and bolt 
heads are covered and present a neat appearance. It will be 
noted that wherever a bolt head comes against the outside of the 
magnet frame, that place is spot faced, that is, faced off so as to 
give a flat bearing surface. 

Details of Feet. Several sections are shown through the 
feet so that their form is determined definitely all over. An en- 
larged view of the bead at the point where the two halves are joined 
is also shown. These sections and enlarged views help the pattern 
maker in laying out his pattern drawings, and are an essential 
part of the drawing. 

Details of Base. The base, Fig. 11, is a single iron casting. 
While this is but a single piece, a great deal of detail is shown in 



MACHINE DRAWING 241 

order that the pattern maker and foundryman will have sufficient 
information. It will be noted that the casting is hollow, with sup- 
porting ribs at intervals to add strength and stiffness, and with bosses 
on the surface where the magnet frame and pedestals are supported. 
These latter must, of course, be carefully machined to give the 
frame and bearing pedestals the proper relative location. This 
plate also shows the shims, Fig. 12, used for adjusting the height 
of the magnet frame in order that the armature may be properly 
centered in the field. These shims are similar in every way to 
those used for the pole pieces, and serve a similar purpose. 

Note in this drawing again, we have an example of the partial 
picture, the base being symmetrical about the center line of the 

machine. 

PLATE I. POLE PIECES 

General Details. The general outlines and dimensions of 
the pole pieces for the fields are determined by the electrical design, 
but they must all be covered completely by drawings so that they 
can be built in the shop. The main fields have laminated pole 
pieces, that is, the pole piece is made up of thin sheets of steel 
punched out to definite form, Fig. 1, enough being assembled together 
to give the required thickness, Fig. 2. The commutating fields, 
Fig. 6, have solid pole pieces of forged steel. Plate I covers both 
of these pole pieces. 

Field Pole Pieces. The main pole pieces must be riveted 
together to form a solid piece, and the rivets must be spaced and 
placed in such a manner as to give the best mechanical construction. 
The pole tips must be shaded; that is, the amount of iron in the 
tips must be reduced for electrical reasons. Note how this is 
accomplished: Each lamination has one tip cut off in a definite 
manner. The laminations are then assembled with alternate 
pieces having this cut tip on opposite sides. The actual amount 
of iron in the tips is then reduced by one-half. The tips are also 
cut back slightly from a true arc, so that the gap between the pole 
and the armature is greater at the tip. 

The manner of holding the completed pole piece in place is 
also interesting. Each lamination has a rectangular hole near the 
top. When they are assembled, this forms a rectangular passage 
through the whole pole piece, Fig. 2. Part of the laminations 



242 



MACHINE DRAWING 




MACHINE DRAWING 243 

also have another hole punched which cuts across the first one 
and runs out to the top edge so that a square hole is formed from 
the top into the first hole, shown by dotted line in Fig. 2. Bolts 
are passed through the frame into these holes and screwed into a 
threaded key, Fig. 3, placed in the first hole. Thus, when these 
bolts are tightened up, the pole pieces are drawn up against the 
frame solidly. In order that there may be some adjustment of 
the gap between the poles and the armature, shims, Fig. 4, are 
provided which can be slipped between the frame and the pole 
pieces, thus bringing the pole piece nearer the armature. These 
shims are provided with slots instead of holes, so that they can be 
slipped in after the poles are in place. The air gap can thus be 
adjusted when the machine is being assembled, without entirely 
removing the holding bolts. 

Commutating Pole Pieces. The pole pieces for the commu- 
tating fields are simpler than the main pole pieces, consisting of 
a rectangular block of forged steel. The corners at the armature 
end are slightly rounded, Fig. 6. Holes are drilled and tapped in 
the opposite end for the bolts which hold the pieces to the frame. 
Shims, Fig. 7, are provided for these pieces the same as for the 
main poles. Pins placed in the armature end are used for holding 
the field coils and spools. 

Dimensions in Tabular Form. It should be noted that a 
number of the dimensions on this drawing are given in tables in- 
stead of being placed on the drawing itself. The reason for this 
is one of economy. Any manufacturer making a number of machines 
of the same general type but of slightly differing characteristics 
finds that some parts for the machines of different rating vary 
only in a few dimensions. By placing these variable dimensions in 
a table a large number of pieces can be covered by the same picture 
and many drawings saved. Of course, the drawing will not be to 
scale for more than one of these pieces, but on simple pieces this 
is not objectionable. The different parts can be distinguished by 
assigning a specific group number to those parts wanted for any 
particular machine. This group will be referred to in a general 
specification covering the machine wanted. Thus in the present 
machine the specification would call for pole pieces according to a 
group in a certain drawing. By reference to this group certain pieces 



244 



MACHINE DRAWING 




MACHINE DRAWING - 245 

would be called for by number; these numbers in turn being given 
in the dimension table, would fix the dimensions of the piece wanted. 
This is a method used in many drafting rooms where many similar 
pieces are used which can be treated in this way. 

PLATE J. MAIN FIELD COILS AND SPOOLS 

General Details. Having completed the pole pieces, the 
fields themselves and the spools for supporting them can now be 
completed. Plate J covers coils and spools for the main fields. 
These main fields consist of two parts — a series field consisting 
of a few turns of heavy copper (in this case one turn), which carries 
the main armature current, and a shunt field consisting of a large 
number of turns of small wire connected across the armature and 
carrying a small current. All the electrical characteristics of these 
coils will be given by the designer — the number of turns for each, 
the size of copper, and such other things as are fixed by the results 
to be obtained. 

Plan and Elevation of Coils. For the shunt field coils instruc- 
tions will be given to the winder by specification, since a drawing 
is not suitable for giving such information. As to the general 
arrangement of the coils and spool, however, a drawing must be 
made. Notice the plans and elevation of two complete adjacent 
poles, Figs. 2 and 3. These show the directions of the windings 
and the general locations of the terminals. The arrangement of 
the shunt field terminals is shown in the two sections through A A 
and BB. 

Series Field Coils. The series field, as stated above, must 
carry the full armature current. The coil, therefore, consists of a 
number of leaves of copper laid together in multiple and wound 
around the spool, shown in side and end views in Fig. 1. In order 
to keep the heating of this coil to a minimum without using too 
much material, proper provision must be made for ventilation. 
In this case, this is accomplished by placing wooden space blocks 
(indicated by small figures 6 and 7) in such a manner that the coil 
is divided into two parts and so that there is space for air circula- 
tion between the collars and the coil. The two parts of the coil 
are riveted together through the space blocks. Dowel pins are 
passed through one of the collars, through the space blocks, and into 



246 MACHINE DRAWING 

recesses in the other collar, so that the coil is held rigidly in place. 
Since the coil occupies only three sides of the spool, a long wood 
space block, shown in Section A A, is provided to fill the fourth 
side. This block is held in place in the spool by wood pins the 
same as the dowels which hold the coil. 

Connections must be made to this coil by copper bars. The 
ends of the laminations are therefore carried past the side of the 
spool, Figs. 1, 2, and 3, and divided so as to form slots for taking 
quarter-inch copper bars. The drawing gives the number of lam- 
inations in each division and the thickness of each lamination, 
as well as the dimension of the spaces for the connection bars. 

Spools. The spool and flanges are next drawn. The spool 
proper, Fig. 14, is of sheet steel. The ends are turned over one- 
half inch to form supports for the flanges; the sides are lapped and 
riveted. These spools must be made to fit the pole pieces and must 
have proper dimensions to take the windings with adequate allow- 
ance for the flanges. 

. Flanges, The flanges are of veneered maple, to give stiffness 
and prevent warping. Note that the two flanges enclosing the 
series coil, Figs.. 15 and 16, are identical except in thickness and 
in the character of the holes for the dowel pins. One plan and two 
sections are therefore sufficient to show both of these flanges. 

The third flange, Figs. 17 and 18, must be different on 
adjacent poles because of the different location of the terminals. 
The difference is indicated on the plan and section, however, by 
showing the location of one notch by full lines and the other 
notch by dotted lines. This makes the specifications just as clear 
and saves time. 

Assembly of Adjacent Poles. An assembly of two adjacent 
poles is drawn to show the location of the flanges, Figs. 19 and 20. 
This is for the benefit of the assembler and is as necessary as the 
other views of drawings for the man who builds the parts. 

PLATE K. COMMUTATINQ FIELD COILS AND SPOOLS 

The commutating fields are connected in series with the arma- 
ture and carry the full machine current. They are therefore made 
of heavy copper somewhat like the series section of the main field. 
Plate K shows these field coils and the spool. 




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248 MACHINE DRAWING 

Commutating Coil. The coil is made up of several turns 
of copper each made up of twenty-two laminations of thin copper 
strip five-eighths of an inch wide and seventy-five-thousandths 
of an inch thick, Fig. 13. The coil is insulated by separating the 
turns with separating strips of veneered maple, shown in the side 
view, Fig. 1. This veneering, being thin pieces of wood glued 
together with alternate pieces having the grain at right angles, makes 
a very stiff firm support, which will not warp or twist out of shape 
when heated. Placing the coils in this way, they are open to air 
circulation all over and are easily kept cool. The ends of the coil 
must be supported firmly from the spool. This is accomplished 
by means of the two copper clips. Notice Section A A, which shows 
how the coil, clip, and insulation are assembled with relation to 
each other. Notice also how the ends of the coils are spread to 
form slots for the connection bars (see left-hand view Fig. 13). 

Spool. The spool, Figs. 2 and 3, is similar to that for the main 
field. The body consists of sheet steel bent to fit the pole piece 
and having the ends turned down to hold the collars, and the whole 
held in place by means of rivets in one side. The collars are of 
veneered maple and are drilled for dowel pins which hold the sepa- 
rating strips. The separating strips, Fig. 4, are also of veneered 
maple and are very carefully dimensioned to fit the coil. The slots 
must have the proper slope and each of the strips on one side must 
be different. 

Assembly Methods Considered as Draftsman's Problem. 
It is possible that one might go over this whole plate without giving 
a thought to the assembly of the coils. For example, on first 
thought it might seem proper to wind the coil on the assembled 
spool. A little thought will show, however, that this would not 
give a good smooth piece of work and would hardly be satisfactory. 
It is almost universally true that coils for electrical machinery 
are wound on forms and assembled afterward. By studying 
the construction as given in this plate, it will be seen how easy 
it is to take such a form-wound coil, set the separating strips into 
place, and slip this down over the spool body which already has 
one collar in place. The other collar can be placed in position 
and the ends of the spool body bent down over the top collar. 

It is true that this work has nothing to do with shop practice, 



MACHINE DRAWING 249 

and yet the draftsman must sooner or later attain a position where 
he sees things from the shopman's viewpoint. The above para- 
graph illustrates how well the draftsman realized the method to 
be pursued in assembling these coils. The spool might easily have 
been drawn so that the labor necessary to assemble it with the coil 
would have been double that necessary as it is drawn. As an 
example of what this means, the following is typical: In a certain 
shop, two similar electrical devices were being made, one for much 
heavier service than the other. An investigation of costs revealed 
the fact that the smaller one was costing twice as much as the 
larger one. Further investigation in the drafting room showed that 
the whole trouble was that the designing draftsman had laid out 
the smaller device so that the principal casting was very hard to 
mold in the foundry and harder still to finish in the machine shop. 
Simple changes in the drawing by a man familiar with shop methods 
made the costs of the two pieces comparable. So it will be seen 
that the draftsman must consider not only the pattern maker, 
but the foundryman, the machinist, and the assembler as well. 

DETAILS OF BRUSH RIGGING 
PLATE L. BRUSH HOLDER, STUD AND CONNECTIONS 

The previous plates have covered all the principal parts of 
the machine except the parts for collecting the current from the 
commutator. Plate L now takes up the details of the brushes 
and the brush holders. As is usual on such machines the brushes 
are made of carbon, Fig. 12. The size of the brushes is deter- 
mined by the designer, as well as the proper number to be used. 

Pigtail. The brush must have a "pigtail", Fig. 11, that is, 
a small cable to connect to the shank of the brush holder in order 
to get a solid electrical contact between the two. The pigtail 
is in this case attached to the brush by a copper tube passed through 
a hole in the brush and through the terminal on the pigtail. Both 
ends are then spun over, so as to draw the terminal up solidly against 
the carbon, Fig. 12. In order that the pigtail may clear the spring 
which holds the brush against the commutator, the slot for it is 
cut out at an angle. Both sides of the brush are recessed so that 
the brush can be used until it has gone clear into the holder, due to 
wear, without interfering with the holding tube or the pigtail. 



250 



MACHINE DRAWING 




MACHINE DRAWING 251 

The pigtail itself is called for in the title table only, the dimensions 
of the terminals and over-all length being given on the drawing. 

Brush Holder Shank. The brush holder shank, Fig. 2, is 
an alloy casting. It must be carefully machined in the brush slot, 
on the face next the commutator and in the hole for the stud. The 
other surfaces are simply ground to give a smooth appearance. 
Note how the shank is split so that it can be clamped to the stud 
by means of a bolt. Tapped holes are provided for the screws 
which hold the pigtail and the spring holder. The thumb screw, 
Fig. 8, for the pigtail, not being a standard machine screw, is 
detailed. 

Spring Holder. The spring holder, Fig. 6, is a rather ingen- 
ious punching, only the holes for screws and pin being drilled. 
Note that this piece is shown in its normal shape, but that devel- 
opment is necessary in order that the dies for the punch press 
can be made. 

The pin, Fig. 5, and lever, Fig. 4, for the spring, Fig. 3, are 
very simple and do not need explanation. 

The above discussion of Plate L has covered the brushes and 
holder completely. Four of these brushes are needed for each 
pole of the machine, or twenty-four in all. These must be sup- 
ported over the commutator so as to make proper contact, and 
the current must be collected from each set and carried io proper 
terminal strips. The brush holders and the shifting device are 
taken up in Plate M. The current-carrying parts — the studs and 
connecting strips — form the remainder of Plate L. 

Current=Carrying Parts. Stud and Insulation Washers. The 
dimensions of the studs, Fig. 18, can be determined from the other 
drawings and from the knowledge that the yoke must be supported 
from a groove cut into the bearing casting. This stud must be 
insulated entirely from the yoke. It will be seen that two shoulders 
are provided. A nut, Fig. 17b, will be used to draw the first 
shoulder up against the yoke in the slot provided. Molded insu- 
lation, Figs. 17a, is placed over the stud between the shoulder and 
yoke and between the nut and the yoke. The stud can then be 
rigidly supported by the yoke but thoroughly insulated from it. 
The other shoulder, with a proper nut, is used for connecting 
alternate studs electrically by means of the bus rings. 



252 



MACHINE DRAWING 




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MACHINE DRAWING 253 

Bus Rings and Connecting Lugs. These bus rings, Figs. 13 
and 14, consist of copper bars bent into arcs of circles so as to 
span studs 120 degrees apart. Slotted lugs, Fig. 15, are soldered 
and riveted to these bars so that these slots will fit over the stud 
and can be drawn up against the shoulder by nuts. Thus three 
studs are connected together by each ring. Note that the lugs 
are offset so that one ring can be assembled with the lugs pro- 
jecting in one direction, and the other ring with the lugs projecting 
in the opposite direction. This gives clearance between the bars 
which will be of opposite polarity. 

Terminal Strips. Terminal strips, Fig. 16, are also soldered 
and riveted to the rings at convenient points so that the external 
connections can be bolted to them. 

PLATE M, BRUSH HOLDER YOKE AND BRUSH SHIFTING 

DEVICE 

Brush Holder Yoke. The brush holder yoke, which is in two 
pieces, Figs. 11 and 12, so that it can be slipped into the slot on 
the bearing when the machine is being assembled, is made in the 
form of a thin wheel with projecting slotted lugs for carrying the 
studs. These pieces are made of cast iron, and sufficient details 
must be shown to enable the pattern maker to provide a pattern 
of proper section at all points. The enlarged sections at the right 
are for this purpose entirely. Notice on this drawing another 
example of a bent section line used to save drawing other views. 
The line B B B is used since it will then take in one of the holes 
in the hub and permit clearer delineation. 

It will be noted that there are two holes in the hub and two 
in the rim which are for the brush shifting device; the details of 
the latter must be worked out before the proper location of the 
holes can be determined. 

Brush Shifting Device. It will be noted that the arrangement 
for shifting the brushes around the commutator, in order to get 
the proper location for good commutation, consists of a shaft, 
Fig. 8, having mounted at one end a worm, Fig. 2, which engages 
the gear or the rack, Fig. 9, mounted on the bearing housing. 
When the handwheel on the shaft is revolved, the worm shifts 
the brush holder in one direction or another, until the proper 
location of brushes is secured. It is necessary, of course, to place 



254 MACHINE DRAWING 

the shaft in such position that the worm engages the rack properly, 
that is, so that the pitch line of the rack and worm are tangent. 
The holes in the brush holder yoke can be located as soon as the 
worm and rack have been laid out; it will be noted that four holes 
are provided, although only two are necessary, so that the shaft 
and handwheel can be assembled on either side of the commu- 
tator, depending upon which is more convenient for operation. 

Worm and Rack. The worm, detailed in Fig. 2, is a good 
example of the double rectangular thread. In order that the motion 
may not be too slow a one-inch pitch has been determined upon, but 
if a single thread were used with this pitch the thread would be 
entirely too deep; therefore, a double thread is used, which reduces 
the depth to a reasonable amount. If the drawing is checked 
carefully, it will be noted that the worm is not drawn to scale, that 
is, the draftsman has made the picture in the most convenient 
way and has used proper dimensions. The threads are not 
detailed, but are covered by a note, giving the number of threads 
and the pitch. The teeth on the rack are, of course, determined 
by the pitch of the worm, so that no further information is nec- 
essary. It will be noted that the dimensions of the rack are given 
in degrees, since the amount of the shift required for the brushes 
would be expressed in this way. 

Shaft. The shaft, Fig. 8, for operating the worm is, of course, 
simply a cylindrical bar of sufficient length to bring the handwheel, 
Fig. 3, to a convenient point. The only detailed dimensions nec- 
essary are those referring to the holes for pins at various points. 

For bearings for this shaft a steel casting, Fig. 6, is used, having 
a stud which passes through the brush holder yoke and is secured 
by a nut. The shaft is held in the proper position by means of the 
worm which is pinned to the shaft, Fig. 2, and a collar, Fig. 5, which 
is also pinned to the shaft and located below the upper bearing. 
The construction here does not require fine work since the brushes 
are only shifted at long intervals and easy operation or freedom 
from friction is not required. The cast-iron handwheel, Fig. 3, 
is of simple construction, with a hub which fits over the shaft and 
is pinned to the shaft. The whole construction is simple enough 
to be easily understood, and great elaboration is not necessary for 
the workmen in the shop. 



MACHINE DRAWING 255 

BEARINGS AND PEDESTALS 

The machine proper, as far as electrical features are concerned, 
is now complete, although considerable work is still necessary or 
the connections between the fields and to the terminal blocks at 
the side of the machine. There are, however, the mechanical 
features of the bearings and pedestals which are taken care of in 
the two following plates. 

PLATE N. SPLIT BEARINGS FOR ARMATURE SHAFT 

General Details. The bearings proper, Figs. 1, 2, 5, and 6, 
are self-aligning, that is, they are constructed so as to adjust them- 
selves automatically to the position of the shaft. This is accom- 
plished by making the bearing casting with a hub on the outside 
which is turned to a spherical shape. The bearing pedestal and 
caps are then constructed so as to fit these pieces into a correspond- 
ing spherical support. This makes in effect a ball-and-socket 
arrangement, which allows considerable adjustment in any direction, 
so that it is not necessary to align the two pedestals accurately, 
either horizontally or vertically. 

Oil Ring Details. The scheme for keeping oil on the bearings 
is one commonly used for machines of this class. The oil is con- 
tained in the receptacle in the pedestal. The bearings have slots 
cut through, which arrangement allows oil rings to rest on the top 
surface of the shaft, the bottom of the ring dipping into the oil in 
the receptacle. As the shaft revolves, the rings pick up oil and 
transmit it to the top of the shaft. Grooves are cut in the babbitt 
metal forming the bearing surface so that this oil can flow over 
the whole surface of the bearing. It will be necessary, of course, 
for the draftsman to detail all these parts and to arrange them so 
that they will be easily constructed in the shop and easily assembled 
at any time afterward. 

Babbitt Metal Linings. It will be noted that the bearings 
are lined with babbitt metal and that the two halves of the iron 
shell are cast with ridges so arranged that when the metal is in place 
it is held solidly with no chance for slipping or turning. This metal, 
of course, is poured into the bearing with the shaft in place. It 
will be seen that the openings in the top half of the bearing are 
so arranged that the babbitt metal can be poured in conveniently. 




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MACHINE DRAWING 257 

It is necessary, of course, to cut away the metal at this point after 
it is cold in order to provide a peep hole and in order to clear the 
slots for the oil rings. The inside surfaces, being shaped to fit 
after the metal is cold, have grooves for oil transmission cut in 
after the bearing is complete. Since these operations cannot be 
shown in the drawing, no information is given except as to the 
metals being used. 

The details of the two bearings are much the same but, never- 
theless, they are very carefully brought out in the drawings in 
order to give the f oundryman and shopman the necessary informa- 
tion. The parts of the 4§X13§ inch bearing are made larger and 
stronger as this bearing is subject to greater strains, being on the 
side where the shaft coupling is placed. 

PLATE O. PEDESTALS AND CAPS FOR BEARINGS 

Pedestal Details. It will be noted, first, that the pedestals 
or standards, Figs. 2 and 13, are built with machined bearing 
surfaces at the bottom where they are bolted to the bed plate, or 
base, which has already been detailed in Plate H. The upper 
part of the pedestal is cast hollow so as to form a receptacle for 
oil, an oil gage, Fig. 5, being placed on the outside so that there is 
constant indication of the oil level. 

Bearing Cap. The bearing cap must, of course, be arranged 
so that it holds the bearing proper solidly in place, and this cap, 
as will be noted from the plate, Fig. 1, is bolted to the bearing 
pedestal. Thus, it is an easy matter to remove the cap and open 
up the bearings at any time. It will be seen that holes, Fig. 3, 
are provided in the top of the cap, which can be used for inspecting 
the oil rings to see if they are revolving properly and are carrying 
oil to the bearings. 

Details for Pattern Maker. It will be noted that the castings 
for the bearings, pedestals, caps, etc., are somewhat complicated, 
and complete information is given in the drawings so that the 
pattern maker can make proper patterns and core boxes for pro- 
ducing these castings. A number of half-sections on the main 
drawings and enlarged sections of cap and foot details, oil gage, 
and oil holes are necessary for this work in order to show the exact 
shape of all the different parts of the casting. 



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MACHINE DRAWING 259 

DETAILS OF ELECTRICAL CONNECTIONS 
PLATE P. ASSEMBLY OF CONNECTIONS 

The next work which will be necessary in the drawing room is 
a layout of the connections between fields and between the bus 
rings and terminal blocks at the side of the machine. Before the 
actual layout of these connections can be completed, however, 
it is necessary to determine exactly how the connections will be 
made as shown in Plate P. 

Diagrams of Connections. Fig. 3 shows these connections 
laid out diagrammatically. An elevation of the machine is drawn 
rather roughly, showing the bus rings, the fields, the connections 
between fields, and the terminal blocks with connections to fields 
and bus rings. Note that the terminal blocks are shown separate 
from the machine and are revolved through 90 degrees in order to 
bring them to the same plane as the elevation of the machine itself. 
This is merely a matter of convenience, so that the connections 
can all be shown on one view. 

Development of Field Spools. Next, a development of the 
fields is shown at the left, looking from the inside of the machine. 
This is to indicate the relative location of the series and commu- 
tating field connections. 

Assembled View of Bus Rings. A small section showing the 
relative location of the bus rings on each side of the brush holder 
yoke is also shown so as to indicate the position of these bus rings 
with respect to the connections. It will be seen that this view and 
the others just discussed are merely diagrams which are provided 
in order that the draftsman may have something to start with in 
laying out the connections. . 

Assembly Drawing Showing Details of Connections. In Fig. 
1, the draftsman has again shown an elevation of the machine and 
an elevation of each of the terminal blocks on the side of the magnet 
frame. The detailed drawings of the fields, Plate J, and of the bus 
rings Plate L, and the amount of current to be carried determine 
the size and number of bars or cables which should be used for the 
various connections. The assembly shows the exact shape of these 
connections and the manner in which the details must be worked 
out in order that there may be no interference between the various 



260 



MACHINE DRAWING 




262 MACHINE DRAWING 

parts. Note how the cable connections between the bus rings and 
the terminal blocks have been indicated only by a line with arrow- 
heads; that is, these cables will hang in a loop, and there is no use 
wasting time or effort in drawing them in completely. 

PLATE Q. CONNECTIONS 

Having completed the assembly layout of the connections, 
the details can be worked up as shown on Plate Q. This plate shows 
each bar of the connections laid out to exact shape and dimensions, 
and represents a very large amount of tedious work. The drafts- 
man must check with extreme care every dimension given in the 
previous drawings which will affect the dimensions of these bars, 
and must be sure in every case that the bars will fit into the proper 
slots or terminals provided for them on other parts of the machine 
and will clear all of the fields, the framework, machine, or any other 
part where electrical or mechanical clearance is necessary. In 
each case, it is also necessary to determine as nearly as possible the 
developed length of the bars so that the copper can be cut before 
bending. The draftsman must also consider the assembler and 
see that the bars are arranged so that they can be assembled easily 
and so that the holding bolts can be slipped into place and drawn 
up without interference. While all of this means an exceptionally 
large amount of work on the part of the draftsman, it should be 
perfectly clear to the student just what method has been followed 
and what work is necessary in developing this drawing. 

FINAL ASSEMBLY DRAWING 

PLATE R. OUTLINE 

General Details. The final plate of this series is Plate R. 
This is a drawing which is entirely unnecessary from the standpoint 
of manufacturing the various parts of the machine, but is indis- 
pensable to the man who assembles the machine either in the factory 
or during installation. This drawing is laid out along the same 
lines as Plate A except that more detail is included and the informa- 
tion given bears in mind especially the assembler. It will be noted 
that the foundation bolts are shown in this drawing, the location 
for these bolts being given so that the foundation can be properly 



MACHINE DRAWING 



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264 MACHINE DRAWING 

constructed and bolts set, even if the machine had not been 
received. 

Coupling Details. Another point which is given in detail 
is the coupling for attaching the machine to the prime mover. It 
will be noted that the dimensions of this coupling have been given 
in inches taken from the detail drawing, and also in millimeters. 
This is necessary since the machine may be for use in a country 
where the metric system is used, and the manufacturer of the prime 
mover might be familiar with the metric system only. 

Terminal Locations. Notice that the relative locations of the 
terminals are shown and that the terminals themselves are marked 
definitely, "positive", "negative", and "equalizer". A table is 
also included which shows the proper size cables for the positive, 
negative, and equalizer leads. In fact, all the information on this 
drawing is of such a nature that the drawing can be given to the 
ultimate user of the machine and can be used by him for assembling 
and setting the machine on its foundation. It will be seen that 
very few of the smaller details have been shown, such as bolt 
heads or holding bolts for the field, etc.; that is, these details are 
unimportant for such a drawing and would require an immense 
amount of time on the part of the draftsman. Time spent in put- 
ting in these details would be a great waste of money and would 
add nothing to the value of the drawing. 

Missing Information Provided in Specifications. If the student 
has studied the plates thoroughly, he will see that there is some 
information which is not given in these drawings. This infor- 
mation, such as the size of wires and number of turns for the shunt 
fields, is given in the form of specifications. In any electrical 
device it will be found that some such information cannot con- 
veniently be included in a drawing. It is also true that there must 
be some sort of master sheet which will connect the many draw- 
ings necessary for showing such machinery; that is, the shop speci- 
fication or summary sheet will be prepared, usually in the form of 
a table. This may include a list of all the drawings necessary 
for building the machine and will contain either the specification 
for such parts of the machine as are not covered on the drawings 
or a specific reference to another drawing which does contain such 
specification. In other words, the manufacturer, in placing such 



MACHINE DRAWING 265 

a machine in the shop to be built, will give to the shopman such 
a master sheet or drawing list from which the shop man may deter- 
mine exactly what detailed information he must obtain in order 
to produce the machine. The practice in this respect varies con- 
siderably with different manufacturers, but practically all of them 
use some modification of this plan in order to have something 
which will connect the various drawings and give proper refer- 
ence for these drawings to the shopman. The plates which have 
been shown in this work are for the most part of such a nature 
that they may be developed independently by the student. Some 
of them may require a considerable knowledge of the principles 
of electrical design, but it is to be hoped that the most of them will 
be developed by the students, since such development will give a 
better idea and a more thorough grasp of the principles involved 
than anything which can be written. It should be remembered 
that the drawings included in this set of plates will show only one 
method of procedure. This method may be modified to some 
extent in any drafting room and does not represent any fixed scheme. 
The general principles of line delineation are followed rather closely 
and the method represented is in use by a large manufacturer and 
can be considered as practical and successful. 



INDEX 



INDEX 



PAGE 

A 



Annular gears 141 

Assembly drawings 36 



B 

Belt holes 127 

Belting 108 

belt holes 127 

cone pulleys 125 

crowning pulleys 110 

general practice 131 

open and crossed belts 109 

quarter-twist belt _ 114 

reversible quarter-twist 116 

shafts not parallel ■. 113 

tight and loose pulleys 112 

Bevel gears . 145 

Black prints, formula for 36 

Blue-print solution, formula for 35 

Blue printing 33 

Bolts and nuts, specifications for 20 



C 

Cams 82 

cylindrical 107 

design of complicated 98 

examples in laying-out cams 85-98 

factors in design and layout 83 

harmonic motion 100 

mechanical action -_ 82 

practical example of complex motion 102 

uniform motion . 99 

uniformly accelerated and retarded motion 101 

translation 104 

variable motion • 100 

Cone pulleys 125 

Crosshatching 6 

Cycloidal gears -_ 136 

design of epicycloidal gears 136 

formation of cycloidal curves 136 



268 INDEX 

PAGE 

D 

Dimensions . 9 

Direct-current generator, design of 222-265 

armature flanges and spider 230 

armature punchings 226 

armature shaft 238 

armature windings 226 

assembly of connections 259 

brush holder, stud and connections 249 

brush holder yoke and brush shifting device 253 

commutating field coils and spools 246 

commutator details 233 

connections 262 

equalizer rings and support 231 

general outline drawing 224 

general specifications 222 

magnet frame and base 240 

main field coils and spools 245 

material supplied to designing draftsman 222 

outline 262 

pedestals and caps for bearings 257 

pole pieces 241 

split bearings for armature shaft . 255 

Drawings, cost of 221 

Drawing, essentials of a good 220 

Drawings, illustrative 220 

bearing stand with cap and boxes removed 60 

bell crank 41 

''broken" pieces and "out-of -scale" dimensions 60 

clamp eye. 45 

connecting rod 46 

crane drum grooved for chain 56 

crank 37 

cylinder head 52 

flange coupling 43 

gear with split hub 46 

hoisting drum 56 

link stud 43 

ordinary shaft 59 

pair of beveled gears 49 

rocker arm and pin 42 

sample letters 61 

spur gear 49 

water cylinder for triplex pump 53 

worm and worm gear 49 

Drawing room practice 62 

Duplex pump plates 163-21 1 

foundation 208 

general drawing 208 



INDEX 269 

PAGE 

Duplex pump plates 

order sheets „ 211-216 

piston rod and valve stem 184 

plunger and valve details 206 

steam chest and valve 186 

steam cylinder 171 

steam end layout 165 

valve motion details 193 

valve motion layout , 189 

water cylinder 201 

water cylinder cap and air chamber 204 

water end layout , 199 

yoke, stuffing boxes, etc „ _ 195 

G 

Gear teeth . 148 

Gears 132 

annular 141 

bevel 145 

cycloidal 136 

general theory 132 

involute gears ._ 142 

rack and pinion _ 142 

H 

Helical springs 72 

Helix 70 

construction of curve 71 

development of 70 

helical springs 72 



I 

Involute gears 142 

compared with cycloidal 142 

design of 143 



L 

Letters, sample I 61 

Lines 2 

center or axis 3 

dimension - 3 

extension 3 

full 2 

invisible 2 

shade _ „ ^ - - 4 



270 INDEX 

PAGE 

M 

Mechanism drawing 69-155 

belting 108 

cams 82 

gears 132 

helix 70 

plates * 149 

screw threads 75 

Mechanisms, study of 69 


Order sheets 211-216 

P 

Pencil drawing m 31 

Pipes and pipe-thread, specifications for 26 

Pitch of screw thread 16 

Plates 149-152 

sketches 63 

valve motion details 63 

water plunger 63 

water valve details 63 

R 

Rack and pinion gears 142 

S 

Scale drawings 27 

Screw threads 75 

conventional representations of 80 

screw and nut 75 

square and v threads, typical forms of 79 

square thread 78 

v thread 76 

Screw threads, specifications for 15 

Sectional views 5 

Shade lines 4-7 

applications in practical work 7 

methods _* 8 

uses 7 

Sketches • 31 

Square thread _ 78 



T 
Tracing. 32 



INDEX 271 

PAGE 

V 
V thread 76 

Views, arrangement of 4 

W 

Whitworth standard thread 80 

Working drawings 1-68 

definition of 1 

dimensions 9 

- illustrative drawings 37 

instructions and specifications 10-30 

lines 2 

plates 63 

preparation details 31 

sectional views 5 

shade lines 7 

views, arrangement of 4 

Working shop drawings — electrical 219-265 

armature and commutator 224 

brush rigging 249 

electrical connections 259 

field frame and coils 238 

final assembly drawing 262 

preliminary layout sketch 224 

Working shop drawings — mechanical 157-218 

duplex pump plates 1 63-21 1 

essential requirements 159 

method of procedure 162 

plan and scope of advance work 157 

plates 217 

Workmen using drawings 11 

blacksmith 13 

machinist 13 

order and receiving clerks , 15 

pattern maker -. 11 



American Technical Society 

PRACTICAL HANDBOOKS FOR HOME STUDY 

OWING to a constant and increasing demand for 
low-priced single volumes covering all phases of 
Engineering, Mechanics, and Business, we have 
published the following practical handbooks which 
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If your dealer does not have in stock the particular title 
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When cash accompanies an order, any book purchased from 
us may be returned after a five-day examination, if it seems 
unsuited to your need. Upon its return, your money will 
be promptly refunded. 



Titles and Authors 



PRICE 

Air Brake L. V. Ludy __ ___$1.00 

Alternating-Current Machinery William Esty 3.00 

Applied Electrochemistry and Welding Burgess-Cravens 1.50 

Architectural Drawing and Lettering Bourne- von Hoist-Brown 1.50 

Bank Bookkeeping Charles A. Sweetland 1.00 

Boiler Accessories Walter S. Leland 1.00 

Bridge Engineering-Roof Trusses Frank O. Duf our 3.00 

Building and Flying an Aeroplane Charles B. Hay ward 1.00 

Building Code F. W. Fitzpatrick 1.00 

Building Superintendence Edward Nichols 1.50 

Business English and Correspondence Chas. R. Barrett 1.00 

Business Management, Part I James B. Griffith 1.50 

Business Management, Part II Russell-Griffith 1.50 

Care and Operation of Automobiles _• Morris A. Hall 1.00 

Carpentry Gilbert Townsend 1.50 

Civil Engineering Specifications and Contracts --Richard I. D. Ashbridge_ 1.00 

Commercial Law John A. Chamberlain 3.00 

Compressed Air Lucius I. Wightman 1.00 

Contracts and Specifications James C. Plant 1.00 

Corporation Accounts and the Voucher System. _ James B. Griffith 1.00 

Corporation Law Abbott-Springer-Gilmore 3.00 

Cotton Spinning Chas. C. Hedrick 2.00 

Dams and Weirs W. G. Bligh 1.00 



Titles and Authors— Continued 

PHICE 

Department Store Accounts Chas. A. Sweetland 1.50 

Descriptive Astronomy Forest Ray Moulton 1.50 

Dynamo-Electric Machinery F. B. Crocker 1.50 

Electrical Measurements Bushnell-Turnbull 1.00 

Electric Railways Henry H. Norris 1.50 

Electric Telegraph, The Thorn-Collins 1.00 

Electric Wiring and Lighting Knox-Shaad 1.00 

Elevators, Hydraulic and Electric J. H. Jallings 1.50 

Estimating Edward Nichols 1.00 

Factory Accounts Hathaway-Griffith 1.50 

Fire Insurance Law E. R. Hardy 1.50 

Fireproof Construction Fitzpatrick-Condron 2.00 

Forging John Lord Bacon 1.00 

Foundry Work Wm. C. Stimpson 1.00 

Freehand and Perspective Drawing Everett-Lawrence 1.00 

Gasoline Automobile, The Lougheed-Hall 2.00 

Gas Engines and Producers Marks- Wyer 1.00 

Heating and Ventilation Chas. L. Hubbard 1.50 

Highway Construction Phillips-Byrne 1.00 

Hydraulic Engineering Turneaure-Black 3.00 

Insurance and Real Estate Accounts Chas. A. Sweetland 1.50 

Knitting M. A. Metcalf 2.00 

Locomotive Boilers and Engines L. V. Ludy 1.00 

Machine Design Chas. L. Griffin 1.50 

Machine Drawing Griffin- Adams 1.50 

Machine-Shop Work Turner- Perrigo 1.50 

Masonry and Reinforced Concrete Webb-Gibson 3.00 

Masonry Construction Phillips-Byrne 1.00 

Mechanical Drawing Ervin Kenison 1.00 

Modern American Homes H. V. von Hoist 2.50 

Motion Pictures Davis S. Hulfish 3.00 

Orders, The (of Architecture) Bourne- von Hoist-Brown 3.00 

Pattern Making James Ritchey 1.00 

Plumbing Gray-Ball___ 1.50 

Portfolio of the Orders (of Architecture) Bourne- von Hoist-Brown 3.00 

Power Stations and Transmission Geo. C. Shaad 1.00 

Practical Aeronautics Chas. B. Hayward 3.50 

Practical Bookkeeping James B. Griffith 1.50 

Practical Lessons in Electricity Millikan-Crocker-Mills_ _ 1.50 

Railroad Engineering Walter Loring Webb 3.00 

Real Property Law A. M. Kales 1.50 

Refrigeration M. W. Arrowood 1.00 

Reinforced Concrete Webb-Gibson 1.00 

Sewers and Drains A. Marston 1.00 

Sheet Metal Work Wm. Neubecker 3.00 

Stair-Building and Steel Square Hodgson- Williams 1.00 

Standard Legal Forms Edward T. Lee 2.00 

Steam Boilers Newell-Dow 1.00 

Steam Engines L. V. Ludy 1.00 



Titles and Authors— Continued 

PRICE 

Steam Engine Indicators and Valve Gears L. V. Ludy 1.00 

Steam Turbines __: Walter S. Leland 1.00 

Steel Construction (Pocket-book Ed.) H. J. Burt 2.75 

Strength of Materials Edward Rose Maurer 1.00 

Structural Drafting Frank O. Dufour 1.00 

Surveying Alfred E. Phillips 1.50 

Switchboards C. C. Adams 1.00 

Telephony Miller-McMeen 4.00 

Textile Chemistry and Dyeing Louis A. Olney 2.00 

Textile Design Fenwick Umpleby 2.00 

Tool Making Edward R. Markham _ _ _ 1.50 

Underwriters' Requirements Dana Pierce 1.00 

Water Supply Frederick E. Turneaure _ 1.00 

Weaving H. William Nelson 2.00 

Wireless Telegraphy and Telephony Ashley-Hay ward 1.00 

Woolen and Worsted Finishing J no. F. Timmerman 2.00 

Woolen and Worsted Spinning Miles Collins 2.00 



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